How to engage my party more creatively in combat?

Just looking for advice here, I've tried a lot of different variations of enemies and while I can definitely make challenging encounters, in the end my party usually still takes the same steps to solve them.

Meet the level 8 party: Barbarian, Summoner, Witch, Swashbuckler, Ranger. They also have NPC companions, but with only 1 active at a time (essentially functioning as another character of their level).

The Swashbuckler trips with most of his actions. The Barbarian, Summoner and Swashbuckler stand next to the enemy until it stands up, so all 3 get an AoO. The Ranger uses spellshots and gets free RK's, the Witch uses utility spells (Slow, Loose Time's Arrow, Life Boost) and gives even more RK's through Discern Secrets. The Summoner is built for massive healing with her Lay on Hands and all Medicine skill feats. The NPC companion is whatever class suits best for the combat, they can switch them out for one of their own actions.

In essence, they're a highly effective party. And most combats become either: - Pretty damn easy - So many creatures it takes forever to solve their turns - Flying creatures which are somewhat harder for them to deal with, but can't make use of them all the time - Creatures with a 2-action "I hit everyone" move that stay down and eat the -2 even if the Swash trips them, which the party survives by the skin of their teeth, but again can't use them all the time and that kind of action rotation is pretty boring - Spellcasters that aren't very difficult to subdue once one of the martials gets next to them and trips

It's not like they've "solved the game" but I noticed that combats are starting to devolve into the same action routines from everyone involved. Has anyone had experience with something like this?

I usually try to cover stuff like special terrain, using verticality, more interesting boss monsters (essentially merging multiple creatures into 1 but with multiple turns), I guess I just haven't used that many hazards but honestly its not like there's that many in the game to begin with. And usually I can't get more alternate win conditions than just "beat up enemy" or "enemy flees", but I'm running Kingmaker and don't want to massively alter the story