Plenty of older guys I play (40's-50's) all rip their fh topspin... as hard as the juniors... they/we just don't get into position to hit that fh as often as the juniors can
That said, if someone is slicing and dicing you to death where you can't hit your fh effectively, what quality of shot are you giving them to allow them to do that to you?
Against a good slicer, and I'd be hitting almost moonballs to get the ball out of their strikezone... or at the very least they can't hit the slice and keep it low if they are constantly hitting at shoulder/head height.
Also, nothing wrong with just slicing a low ball back..
Something else to think about... for folks just learning topspin (eg. high 3.5 to low 4.0), for some reason, forget about hitting for depth, and think the spin they just learned is enough to win the point (worked at 3.5 and 4.0)... but when they come up against someone that is used to hitting that spin... that topspin fh ends up being a liability, because it feeds their opponent sitters at the baseline. in this case, if you're slice is consistent enough to place deep, it's probably a better shot, until you can get the same depth with your fh.
Lastly, the question, to me, really sounds like, "If one is not in the best tennis shape, is topspin or slice better"... obviously the real answer is to drop some weight, get into shape, etc... but if they wasn't an option, I'd probably play a touch game, where I'm dinking you all over the court with lobs, droppers, occasional drives, etc... and I'd position myself in no-man's-land to minimize my running, but I better be pinpoint accurate, because if I leave just one sitter, the point is over.