Well, I wouldn't say we've only seen a few Minicons- the most recent cartoon in the Aligned continuity family (Robots In Disguise 2017) has two Mini-Cons on the main roster, a rather lengthy arc about a different group of mini-cons, and establishes that Soundwave's tapes are mini-cons. As for Combiners, well, that's the subject of the most recent storyline- the Stunticons as Menasor vs. Team Bee's new combiner form.