Also speaking of Mewtwo being able to keep people out, so few people understand just how safe his dsmash is. Its only got 22 frames of end lag.
To put that in perspective;
Mario ftilt: 25
Falco ftilt: 20
Marth jab: 24
Sheik dtilt: 24
Zss ftilt: 21
Mewtwos dsmash is unpunishable on block to many characters who lack long-range tethers or without top-tier dash attacks and dsmash whiff into dtilt is safe on block if the enemy runs in to try and punish the dsmash but shields the dtilt. It's pretty good
Really late, but Falco's Dtilt would have been a slightly better example; it's frames 7-9 with 27 total frames meaning it only has 18 frames of recovery - Ftilt should be 19 -, it's -17 on-shield, -10 after shield drop, and +2 on-hit at 0% with the disjoint while the close hitbox is -16 on-shield, -9 after shield drop, and +10 on-hit at 0%. It's probably the dumbest Dtilt that kills, the disjoint combos into itself at low percents, sets up, is fast, and has little end lag. Also, Fox's Ftilt would also be a better example; it's frames 6-8 with 23 total frames meaning it only has 14 frames of recovery.
When we talk about recovery, the time in frames between actives frames and another action, you kind of have to factor in not only the startup and total frames, but active frames as well. Mewtwo's Down Smash is frames 21-22 with 43 total frames. That's 21 startup, 2 active frames, and 20 recovery frames for 43 total frames. If you don't factor in active frames, then it seems like it only has 21 recovery frames which isn't much. Contrast this with ZSS's Down Smash which is frames 20-24 with 41 total frames. ZSS's Down Smash has a startup of 20 frames, 5 active frames, and 16 recovery frames for 41 total frames. Now what happens if you don't factor in active frames? ZSS's Down Smash ends up with an inaccurate 21 recovery frames. The theory is that because Mewtwo's Down Smash kills, it should have less active frames and slightly more total frames versus ZSS's Down Smash that does not kill because of its weighted knockback. The issue here is how that translates from 1v1, 2v2, 3v3, 4v4, FFA, etc. In theory, Mewtwo's would probably be better in 2v2 and above since he can suddenly kill you or bait you in chaos while in 1v1, it's not as effective since while it's a kill move, Mewtwo's in the spotlight, it's still slow, and lacks the ability to setup like ZSS's.
Also, you'll have to factor knockback as demonstrated above and then some more like separate hitboxes. So, Yoshi's frame 3 Nair might have 22 active frames and 19 frames of recovery for 44 total frames, it has 3 separate hitboxes, a clean 3-5 hit, a 5-11 hit, and a late 12-25 hit. If you're only looking for the recovery between his clean hit and total frames, then it's actually 38 recovery frames since the clean hit only has 3 active frames. Even further, there are moves with inactive frames along with recovery like Zelda and Samus's Up Smashes have about 4 frames between each hit, however, since they're multi-hits, you just include everything as recovery since you're not really going to care if you hit with the Nth hit of a multi-hit move compared to hitting with say, the clean hit of Captain Falcon's Bair versus the late hit.