Bit of an update to this then.
Played it last night using my HRAP with all the Turbo functions set to max. I fared 200% better than I ever have done before. I have a Unibios, so I set it to infinite credits. I definitely used more than 4 credits, but I managed to get through the game, right to the end credits. Turns out I was using, what the game seems to consider, that last boss (Master Barnes). I chose him because of his Robert Garcia esque kick special I saw him do on an attract demo. Maybe that helped too?
Before this, I'd always struggled to progress beyond the 3rd or 4th match.
I will say though that the CPU still pulls off plenty of bullshit to mouth off at your TV about. One of which is whittling your opponent down to ZERO health, pinning them, and them kicking out. Not once, but several times, quite often to have that last 'illegitimate' kick out spell your demise as they rush you down and then pin YOU with your zero health. No 2nd chances for you, and believe me, I've tried!!
And, as you've suggested, although you win the majority of grapples (to be fair) there are still quite a few WTF moments when they overcome your grapples several times in a row. Bearing in mind that I am effectively 'cheating' using Johnny Five levels of turbo input.
Overall, it was definitely more enjoyable. Wouldn't touch it without provisions for Turbo settings though...