Doesn’t help after the event, but my philosophy is ‘He who pays the DJ calls the tune (quite literally!)…” – so, refer the whingeing guests to whoever paid you to play only 80s/90s/00s music!
Reading your Post, I would add one caveat… who was actually paying for your services as a DJ? The Groom/Bride-to-be, or the ‘Planner’ you refer to – I’ve heard of people using wedding planners, but not engagement party planners! My guess is, it was the planner trying to look good to the Bride & Groom, at your expense! I would always seek permission/guidance from the client directly in this sort of situation.
If YOU can’t get to the client directly, tell the guests to get the client to speak to you…