It depends on the situation. Neither set is truly better than the other.
Yes, overall CB Scizor > CS Scizor.
Scarf Scizor still has utility and can check other threats that CB Scizor can't.
His overall Utility is nerfed when you put a scarf on him because his Utility stems from hitting hard, not hitting first. Let me elaborate:
Power on Uturn > Having Uturn hit first (because you use Uturn in situations where you generally aren't threatened to be killed if you move second). Because BP is priority, it benefits less from Speed than Power.
Basically, in situations you need to use BP, you want it to be as powerful as possible. If you can, you shouldn't put yourself in positions where your Uturn HAS to hit first. Hitting harder with those two moves is more important than hitting sooner with Uturn IMO.
You still add damage and have the switch advantage with Scarf Scizor. Arguably it's better because Scizor isn't taking any damage other than entry hazards because you're switching into something that resists the attack launched at Scizor. If you were to use CB, then Scizor's the one taking the hit, limiting the number of times it can switch in.
Ok here's what I'm thinking based on what you are trying to say:
Opponent has Pokemon. You expect a move Scizor resists so you throw him in. He takes this hit. Now based on what set you have, you play the situation differently. You think CS is better or just as good because you will get in Uturn first (assuming they aren't faster than you) where as I think CB is better because you hit harder and you shouldn't throw him into situations where you HAVE to have Uturn hit before them. Now here is where it gets interesting. Your CS Scizor will get Uturn in first, and if they stay in then your switch has to take the next attack. If they are a threat you wanted to BP instead, well enjoy the loss of power. On the other hand, my CB Scizor will probably have the power to deal with that threat with BP, or if I use Uturn and they stay in, Scizor takes the hit (remember you aren't trying to have him in situations where he needs to hit first) and then the switch comes in safer. Now if they switched, then CB wins because it does more damage and having a faster Uturn is irrelevant.
For his other moves, what threats are you trying to deal with that need you to have a faster Superpower or Pursuit/Night Slash? Most threats that you would want to be faster than with those moves, you won't be able to guarantee the KO without the power boost, or you are already fast enough with the CB set to take them out anyways. Why run a Scarf to deal with Gengar/Latias with HP Fire when you can run Tyranitar for those threats better?
However, having two Choice users in that way limits your team. Scarf is more useful in some cases because guaranteed damage is better than no damage at all. Let's say you were up against a Gengar without a Substitute. If you were CB, you have to choose 50/50 between Pursuit and Bullet Punch, both of which could end up with your Scizor dead/at a disadvantage if the Gengar has HP Fire. However, with Scarf Scizor, you can just freely Pursuit and take care of Gengar if it's suffered a bit of residual damage.
What if he hasn't suffered that damage? Now your set is undeniably worse at trying to handle that threat. If there are hazards or if he has taken some damage, then ok sure you get the kill with Pursuit. But you have thrown away SO much just to guarantee that one kill that it's not worth it overall.
Also factor in this: let's say that Gengar himself has a Scarf. What set handles him better? CB lol. Not saying that Scarfgar is common, but just another point that CB Scizor is almost certainly better than CS.
Name me one other Pokemon that can check Gengar, Azelf, Starmie, Tyranitar, Infernape, Lucario (including Bullet Punch versions, something Scarf Tyranitar can't do), and non-Scarf Heatran. It has its place in the metagame.
Scarf Salamence. Kills all of those threats (assuming they aren't running a scarf as well, in which case CS Scizor can't handle them all himself either). Scarf Machamp actually could as well assuming they weren't running CS as well. Scarf Infernape could cover just about all of that as well (Starmie would be a pain, everything else would probably fall to it.
Some of those threats CS is covering with a faster Super Power/moves besides Pursuit, which doesn't take into account the opponent switching where if they switch, generally it's better to hit harder than faster. This, and some of your gameplay moves become a bit more obvious. Lucario for example, there is no set besides Agility and CS that you will outspeed him. If you switch in Scizor into a Lucario, what's he to expect? If he's smart, he figures either you are running a CS set, or the offchance that it is a mindgame and you are running a Swords Dance set and you expect him to switch thinking it is CS. You know what covers them both? Switching. Meaning that your free attack that hits the other pokemon is now gonna be noticeably weaker.
Scizor has more useful resistances and doesn't bring sandstorm along with it, causing your fragile sweepers (like Salamence) to become even more fragile. Additionally, there is no reason to compare non-Scarf Tyranitar to Scarf Scizor, as they are so different that the playstyles would be completely different. Furthermore, Tyranitar without a Scarf still risks getting burned by Rotom-A, KOed by Hydro Pump from Starmie and Focus Blast from Gengar, so it would still need a Scarf to threaten those Pokemon.
Scizor can't handle Rotom H, Tyranitar has a better chance of handling him scarf or otherwise.
Tyranitar can take some hits on the Special Side. You can make a set with him SD Beefy and made to take out Starmie, Latias, Gengar, etc. IF you need those threats gone, you are better off reworking Tyranitar to cover them instead of reworking Scizor to cover them. You do NOT need a Scarf on Tyranitar to cover those threats. In reality, you can cover whatever you need by running either a beefy CB set with SD EV's, or you go the full route of SD ev's and SD + Nature for additional protection (along with some more Health EV's). Basically you make him so beefy that most pokemon he aims to take out can't 2HKO him while he can still 1HKO them.
If you are afraid of HP Fire Gengar, Latias, Starmie, or whatever, run Tyranitar suited to meet those threats instead of Scizor (Actually you can do this with Metagross too if you want, even HP Fire threats yes). Why? Because Scizor handles those pokemon with CB if they DON'T run those sets. By running a CB, you REQUIRE them to have that move (HP Fire or some attack that is used specifically against Scizor) or die. If they do indeed have it, well Tyranitar/other Pursuit user takes care of it.
Pros and cons
CB:
Pros:
- Hits harder
- BP hits with Priority, so generally no need to have it any faster
- Uturn is a move DESIGNED for scouting and doing as much damage as you can with Scizor. It is not meant for situations where you NEED it to hit first or you die.
-Counters most pokemon that CS Scizor handles unless they run a specific move/set to counter you
-Assuming you are using Uturn correctly, you want Scizor to take the non lethal hit instead of the counter/switch Pokemon. Much harder for your counter/switch to do their job when they have to take a hit, where as Scizor doesn't mind since he's gonna hit like a bus of fat people anyways
Cons:
-Pokemon you usually counter/severely threaten will beat you with certain moves or different builds designed to handle CB Scizor
-If you are trapped, say by Magnezone, there is little/no hope of outspeeding him with the SuperPower/Pursuit you are stuck on. No chip damage on him
CS
Pros:
-You hit faster
-You can kinda cover Pokemon that go out of their way to cover CB Scizor. This is mitigated slightly by the fact that you can also run other Pokemon besides a CS Scizor to cover those threats but it's still a somewhat valid point
-If trapped, you have a better chance of getting off a hit of any kind before dying
Cons:
-You lose the ability to serve as a last resort to some powerful sweeps that CB Scizor sneezes at and they die lol
-You lose the ability to hit as hard
-Even with a Scarf, you are not guaranteed to outrun certain threats you wish to cover, where as other Pokemon can cover those threats without needing to worry as much about their speed
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