Lugh, Iris, Tish, they’re all pretty solid picks in their own right. I’ve stated their strengths a lot, so here are some weaknesses:
Lugh has the issue of dying quickly. That’s quite obvious I thonk.
Iris will suffer in content that doesn’t allow her to spam her skill 3.
Tish is basically a supporter for the steroid himes, albeit a really good one. You lose the least with her, but you probably need more good himes to gain overall... that’s assuming you don’t have good light SSRs already.
Of course, as is obligatory, do consider a dick pick if logical decision making fails, since all 3 are considered pretty essential for a light setup anyway.