I don't think doing KBD fast is a real deal breaker to be honest, If I just hold the 2nd back input for a little while as Bryan on 2p I get max distance on the backdash and I am still able to do the cancel at an adequate pace, the time spent holding db in during backdashing and attempting to move way beyond my ability is reduced and I can just hit and hold back as soon as I see the opponent move forward inside range. You can also just backdash twice into a sidestep and repeat and it serves as a good whiff inducer as well, or just crouchdash twice with Mishimas then sidestep.
The motion for legitimate KBD with sway characters with pad on 2p is something that feels hella counterintuitive as the "legit" method is to pronate your thumb so the front side of the last knuckle hits the db portion, I don't think I am ever going to bother learning to do it that way and just do bb - d - bb - d as in I'll hit double back every time just to make sure even though I am sliding after the 2nd back input from b to db or d.
With Mishimas I am always of course going to do the lazy reverse wavedash method of backdashing. Even then you just gotta get into the groove of the "gallop" and not attempt to do it too fast and you cancel the backdash when it's done. As fast as you need to wavedash or backdash cancel you can practice trying to get some speed into it but that eventually leads to less control and a shortened backash, then in real matches you can do it slower and have full backdashes with full control, as in you are actually able to hit electrics if you recognize a whiff rather than exerting yourself by backdashing as fast as you can and moving outside of range to actually punish anything and you are also able to block. If you have a problem of getting hit out of backdashing with mids then that is a clear indicator that you are fucking up the cancel and looking to autopilot too many backdashes in a row when 3 consecutives is the maximum you really need. The 2nd back input on the first backdash absolutely must be held for a short period of time, otherwise you eat these sort of "chasing sequences" like Lee doing a single d4 (you duck, look to low parry, then start backdashing) then the Lee player does blazing kick right after it. If you eat the blazing kick during your backdash it means you crouch cancelled the first backdash without holding the 2nd back input, there are also other sequences like Heihachi's df1 on block into uf3,4 and if you backdash once again after blocking the df1 and crouch cancel the first backdash instantly, there is a good chance you'll eat the uf3,4.
Oh and in regards to wavedashing, when I played with AC the first time (AC Crawford on FB, you see him post on Kor's Tekken Academy every now and then, the dude with all the pervy semi porn sites liked on his FB and no profile picture of himself lol) he could practically light dash into EWGF but he had no defensive control. I don't think anyone who does it that fast has real control and is able to block when needed when approaching the opponent, you can just chuck out quick moves like Bruce/Josie uf3+4 or Bryan fF2 and those are gonna hit the lightdashers out of their wavedash, because they are used to people just freezing and respecting the electric or them just beating everyone out of everything simply because they have an extremely rapid interval of df's in their wavedash and they have the option to choose to hit 2 at the exact correct moment. I think that's like an extreme case of outstanding execution being a crutch and a replacement for solid, basic Tekken play. You simply can't go in from almost fullscreen and wavedashing all the way to the opponents face and expect to make contact without being interrupted or stepped. All forward movement telegraphs an intent to commit to an attack.
