Stingers and leelue have covered most of these two. You're outright wrong with everything concerning Mewtwo, and it's painfully obvious to anyone that has actually bothered to compare the two recoveries (which I did for my own edification four years ago) that you have done none of your own comparisons). And, speaking as a fellow Samus main, I must say you vastly overrate a lot of Samus's options. Samus has no solid way of reaching the ground when someone is threatening her from below. She can threaten them with aerials, but her dair sucks, and her nair is outranged by a lot of uairs. She can use bombs, but there's a very punishable moment right as Samus leaves the first bomb animation that makes air raids unsafe at all but the highest vertical spacings. I say this having played as Samus and against Samus. Her safest option is to air control all the way offstage, then recover from the side. Mewtwo at least has the option to teleport through someone who's overzealously approaching from below.
I don't think you really know what you're talking about, especially if you're gonna say her dair sucks. The move has only 7 frames of landing lag, like all of her other aerials, and it has a good hitbox. Samus can safely dair an opponent's shield and upB right afterwards. Sure, as I said before, this isn't a great option, but saying "her dair sucks" is a sore understatement of Samus's capabilities. Samus may be vulnerable during small portions of the bomb animations, but that's what bomb mixups are for. Samus can bomb
on reaction to many approaches from below and she will bounce off the opponent or even their attack without taking any damage. You can't just bomb repeatedly and unwisely. I went through a 'phase' where I tried to pick up Mewtwo as a fun secondary (never came to fruition), but I did indeed use him a bit, so I'm aware of his options while recovering. I admit that Mewtwo's recovery distance is really good, but his options really aren't.
Judging by join date, I have three years of experience on you, specifically as a Samus main. I'm not sure where you got the impression I'm inexperienced with the character.
Because join date is indicative of when I actually started playing Melee competitively, right, despite all the years I spent lurking without making an account? Besides, Samus's meta was somewhat irrelevant earlier than 2009. So many things have been developed, so time spent playing the character so far back is not as important as time spent recently and now. The character is to be re-learned as the meta advances. I, myself, went over and effectively 're-learned' my own Samus playstyle at least twice since I picked up the char. I got the impression that you were inexperienced from the comments you made.
Edit: Back before 2009, it was a fine strategy for Samus to pressure shields with jab > spot-dodge > jab. That shield pressure strat has since been replaced with the superior pressure strat jab > crouch > jab, with the spot-dodge variant remaining as a mix-up to be used sparingly. New and old Sami alike should be aware of this new meta because it is a more recent development. Being an old Samus does not give you any extra perks in this regard.
That's why I said "primarily." There are other uses for Screw Attack, but most of them are mostly as a mix-up that keeps her other options potent. They're not something you can rely on. Like you said, "There are better options." The only time you'll see a Samus main use upb more than another option they have in a given situation is when they have no other option.
You can't rely on any aspect of most recoveries other than distance. That goes for Mewtwo, as well. The only recovery that has multiple truly reliable aspects is Jiggs. Saying "The only time you'll see a Samus main use upb more than another option they have in a given situation is when they have no other option," simply is not true. As I just said earlier, I may go for a TC off of the Screw Attack if I see the opponent standing open on/near the ledge or hanging on it without invincibility. That doesn't mean there weren't other options. The option to sweetspot the tether is virtually always there.