I don't know about those numbers, because f-tilt->u-tilt definitely is a true combo vs. Wario (and I think 4 means the window is too tight but that's just not the case). The rest of the options seem kinda pointless (snake has better options for getting a C4 stick, dair->grab is a TC, etc.). In my testing (I was too excited about this lol) I found that the f-tilt->u-tilt is a TC (barring crouch cancel) on:
Really tight timing: Wario, Yoshi, Dedede, DK, G&W, Pikachu, Pit, Charizard, Squirtle, Snake, Sonic
Pretty lax timing: Zelda, Kirby, Luigi, Mario, Marth, Mewtwo, Ness, Peach, Olimar, Ivysaur, Ice Climbers, Jigglypuff, ROB, Samus
I found these through 1/4 speed in training mode. If they hit the ground it's considered a no go (this gave my false positives when I did it full speed I found out). Our findings tend to agree but some of yours seem just a little off, to the point that they're actually misleading about what follow-ups are possible. Ike and Sheik doesn't seem possible whereas Wario definitely is. Those I find to be "tight timing" seem to be those closest to 5 on your list, though, so it's good work overall. I don't really think it's useful against the top portion (some of them like DK and Snake actually surprised me) because of how difficult it is to execute, but characters like Zelda, Mewtwo, and Samus die to this SO EARLY and they're some of Snake's tougher matchups, so simply getting a quick C4 into a dair->f-tilt->u-tilt combo could certainly make it a lot easier. I actually made predictions before on these and only got one (Pikachu) wrong so it's pretty intuitive as well. All about fall speed, most likely.