Kel, you need to get more comfortable with Snake's projectiles. You can swat away at up smashes (and how you do so is dependent on the situation). I think the curse of swinging is also apparent here, you didn't really need to be throwing out your sword like you do, usually really preemptively (so you would trade with snake's back air rather than just wait a micro second more considering punshing snake as he LANDS is a lot better than trying to continue a non-guaranteed juggle).
In recent times I've thought about up tilt a bit, and I see you were using it quite a bit with relative success; but you would trade hits too often with it. In recent contemplations I really think that downsmash does just as much as up tilt does in terms of the punish and allows you to move into a lot safer of a position than trying to get utilts would. Taking back airs on your shield continually isn't the type of trade that you want to be doing when you're only punishing with dancing blade, if you're getting your shield destroyed like you were you need to reset to neutral and wait for it to come back up. If you get more confident with fairing those back air landings on shield (probably full hop) you'll at the least be continuing the pressure. Also you need to crouch more, rather than just plainly shielding, ally abuses this against you with footstools or those shield ****** bairs, remember that crouching is reducing you to about 40% of your size and has no lag between the animation and shielding. I don't think you should be throwing out aerials after Ally takes out a nade as a precaution to dash attack at the distances you're doing it.
Your best bet with nades is to always keep count and always be in neutral situation as most throws of nades are really really really easy to power shield, with the forward throw one going over your head while crouching (and the ones that you give too much respect to that are thrown out defensively IMMEDIATELY are easy to instant throw back rather than acting like you need to be afraid for the next 4 and a half seconds) and give you significant **** advantage, Snake has no frame traps on you with anything if you power shield the nade throw, in fact it generally puts Snake at the disadvantage due to it's likelihood of explosion and the fact that nades usually bounce back after powershields. I think your fear of dash attack really took control of you although Ally barely used the move (in the first match). I like your use of first hit nair, it's something I've been working on lately too and it got you a lot of free grabs or frame advantages that you made use of :D
When it comes to Diddy... I'm by no means an expert on it... but you want Diddy throwing nanners at your shield. When I play the MU all I think of is "can diddy fair right now and hit me?" and if my response is yes I jusst do whatever I can to avoid it and then punish them for their otherwise laggy hurtbox massive extender 3000, and it works until they start doing things other than fair (but only like 2 diddys in the world choose not to fair so whatever). When you hit Diddy's shield you always do something immediately after rather than waiting. A lot of your hits on shield in the match that I watched was without diddy having a nanner, and he would do something like spot dodge or roll and you'd always immediately throw out an utilt, or aerial or something. The way Zinoto used his jumps against you really screamed to me "JAB AND FORWARD TILT OPPORTUNITIES".
In a summary type of way. Move away from up tilting like you are. If you're going to continue up tilting, start to get comfortable with crouching before hand so you aren't always trading with people. If you become more comfortable with down tilt you'll also start to see the great opportunities for down smash (as they will both hit in the exact same situations) and be safer in your punishing of landings. The key point to down tilt is that the tipper hitbox extends really high above the ground, so you don't need to be so worried about their vertical displacement as you currently are.
Also stop sh dairing. JEEEZ. And learn to dolhpin slash regrab, that gets you gimps against diddy's recovery more than fall back fair or db1 will ever do.