Oh no - not all the time, of course not.
I find plinking all three punches makes a substantial difference in terms of reliability though. Having said that, I landed a healthy amount of (lucky) wake-up demons on seemingly well placed EX balls from a Ryu player recently that saw me take advantage of the brief invulnerability the demon’s startup enjoys. This of course was followed by me yelling out loud “oh you lucky bastard” because I know full well how small that window actually is
I find it helps to pre-enter the punch portion (for me by plinking) of the demon and then simply press b+lk+fp on reaction thereafter (or not) if I feel its worth going for - e.g. if you see Ken wind up for an overhead, or Ryu try and plough in with his gut-punch. The latter especially as he tends to yell out a cue as if to remind us he’s putting himself at risk.
My point is that mashing out the demon and ‘hoping’ it lands strikes me as unnecessarily risky. I find when using Akuma that my approach is a lot more calculated due to how severely we can be punished combined with capitalising on openings (for me) to be something I make every effort to be precise about which rules out mashing for me. Frankly when faced with situations where the end result looks risky I’ll often opt for a teleport or simply block. With demons though sometimes you can get a feel for your opponent and you know full well he’s going to do something dumb to try and molest your wake-up where a well practised (and therefore reliable) demon response makes a worthwhile option.
As a flip-side to all this though, I’ve had a sparring mate mash out demons while I’ve been ripping into him with combos. The idea from his perspective is that if I screw up, he gets a demon. If I don’t, he’s subject to the combo is doing anyway. A few times its really worked in his favour due to me fluffing a FADC while he’s still grounded and of course I’ve eaten his demon. Frustrating.