Other way around.
Just because you expected even faster WHDLoad performance with an accelerator and didn't get it because of how the games were coded once-upon-a-time, ACA500 is a bad WHDLoad machine? No, only with an accelerator installed. As you say yourself, you can disable it and the full-framerate games work.
However, if you try those with no CPU acceleration, you find my claim that WHDLoad wasn't made to play A500 games on A500 is true, and they start to stutter. So the only option right now is ACA500 or a vintage GVP accelerator or similar. These "tight" games are far from all the games there are, of course. All other games will run fine.
So the Kipper2k card is good but not perfect and ACA500 is good but not perfect. With the right A500(+) setup however, the ACA500 can be and the Kipper2k cannot.
As for memory size, look at my two videos (before and after the WHDLoad 17.2 update) for how to get them running with the admittedly unfortunate RAM size on the ACA500. (As in, 1M more and you could just install any WHDLoad setup and go, and my videos would be obsolete.) Now it is as it is, and so I made the how-to videos.