There's a ton of items that give you the effect of war caster without having to take the feat. Apparently larian REALLY wanted to ensure nobody took any feats other than ASI.
I kinda like that Larian loaded so many passive-feat gear in the game; allows you to plan builds around those items for future runs.
Reminds me of replaying BG2 as a Kensai/Mage and remembering to go straight for Celestial Fury.
Plus build enabling uniques are
What you described is not build enabling, though. More like making builds meaningless.
They effectively buy you feat slots so you can make synergies that were otherwise too build expensive without.
This way you can make more complex builds.
But yeah I get what you're saying, if everything is put into gear the specific class abilities/feats selections become less valuable; which is true if you don't build beyond what those combinations have to offer.
There's the more direct build uniques that do things no class can do organically.
I'd actually go further and say that not even Celestial Fury is a build-enabling weapon.
Its a cool weapon, sure. That will do nasty CC and bonus damage to enemies with some frequency, given the number of attacks you're gonna reach.
But its still just "attack and kill a single target faster" - with CC it in the process if lucky.
Compare it to Deadfire: Hand Mortar and Fire in the Hole on a monk: suddenly your monk Stunning Blows/Surge stun all enemies in an aoe (twice), rather then being single target; the aoe is also a lot bigger due to your Duality: Intelligence. Similarly on a rogue: now your single-target DOTs and debilitating attacks became aoe.
Or Kitchen Stove on an Ascendant Cipher: now your Thunderous Report opening strike vs mobs will always fill your Focus and put you in Ascended state to spam-cast your best Powers on combat start (and you could further extend that state with a cleric's Salvation of Time buff).
Or Grave Calling with Skeletal summons - creating party friendly Blinding, Paralyzing and damaging zones, that also continuously fill your Focus if you're a Cipher (or party unfriendly, rapidly spreading, multiplying, graphics card melting death zones with a Confused Cold-Resistant Pale Elf Berserker).
Or a more specific, late game and limited case: Engoliero de Espirs and Deltro's Cage helmet for my Turn Based Blood Mage/Assassin - who'd nearly knock himself dead with Chain Lightning on self to get a deadly 90-120% Lightning lash, full buff with wizard Free Action buffs, recover all spell slots via Blood Sacrifice, get powerfull bonuses from low health when alpha striking... and still be at full health vs mobs instantly after killing an enemy due to Blade Feast proccing off spell kills (with frequent Blade Feast kill cascades on lower health enemies from aoe spells).