yusuke and kuwabara are brawlers in terms of combat it would be a joke to say they could even touch ranma
Brawlers? Maybe as their base, but they've also had formal training on top of that, what with Genkai and such. (And anyway, it's not like being a "brawler" means you don't know how to fight; Ryouga's easily more of a brawler than those two are, and he still manages to "touch" Ranma quite often. In general, it's not a good idea to sneer at fighting abilities simply because they're not learned in a dojo.)
In any case, to the original point: how their "spiritual strengths" compare depends on where in the series you have them intersect. Ranma's spiritual strength would indeed probably exceed an early-series Yusuke--he didn't have much but the Rei gun, at that point. But on the other hand, by the time you get to the Dark Tournament and beyond, YYH starts escalating into crazy levels of power that Ranma can't even begin to scratch. When you get into stuff like Yusuke and Younger Toguro obliterating whole swaths of demons with no direct attacks at all, just by standing in the same freaking
stadium with them while running their ambient battle auras at something approaching full power... well, comparison gets a little silly, at that point. (And
then Yusuke goes and unlocks his demon heritage... oy vey.)
So, yeah, basically I'd suggest going through and picking your time and place to jump in, since there's a whole gradient to chose from. Actually, a good spot to have them meet might be when they first go to Genkai for training, especially since that's something Ranma would likely be interested in as well. And if Genkai takes an interest in him too, you could use that mechanism to avoid having him get left behind as things escalate.
(But then, of course, I've no idea what your overall plot is to begin with, so that could be completely unworkable. Just what occurred to me, in passing.)