Heavy armor isn't inherently passive - you're just hitting the point where vanilla Skyrim's difficulty scaling completely falls apart. By 25-30 with heavy armor perks, yeah, you've basically won the game.
A few actual fixes:
Requiem is the obvious answer if you're willing to overhaul difficulty. It completely rebalances armor, enemy scaling, and perk progression so you're never unkillable. You'll actually need to use positioning, blocking, and tactical decisions even in full daedric. Fair warning though: it's a lot of setup work in MO2 and you basically have to commit to the whole thing - not compatible with a bunch of lighter mods. But if you're already in the Creation Kit world, it's worth the investment.
If you want to stay closer to vanilla, try Wildcat (the combat overhaul, not Wildlander). It makes blocking matter, adds stagger mechanics that actually punish you for face-tanking, and scales enemy damage properly. You'd still need to pair it with something like Morrowloot or a mod that stops enemies from being trivial, but it forces engagement without a total conversion.
Or honestly? Just crank the difficulty to Legendary and stop taking perks that increase armor rating. Sounds dumb but it actually works - skip Conditioning, skip the heavy armor perks that give damage reduction, and focus on weapon perks and utility stuff instead. Makes you rely on blocking and positioning rather than just stat-checking your way through dungeons.
What's your load order look like right now? Might be easier to diagnose if we know what you're already running.