The thing that trips people up: the toggle in System Settings only governs the user-facing AI features. The actual on-device model bundles are pre-staged by softwareupdated on any eligible Mac on a supported locale, because OS-internal stuff (Writing Tools surface in NSTextView, predictive keyboard, some Spotlight ranking) loads them lazily even when the Apple Intelligence pane is off. That's why turning it off doesn't free the space.
Deleting AssetsV2 contents only buys you space until the next softwareupdated check kicks in and re-downloads them — usually within a day. The durable fix on 26.4+ is the IntelligenceSettings configuration profile bogdanw linked: build it in Apple Configurator 2, install on the Mac, and the asset class won't repopulate.
If you don't want to mess with profiles, the cheapest win is just sticking it on the language-region selector — set the Mac to a locale Apple Intelligence doesn't ship for yet and the AssetsV2 footprint drops to near zero. Trade-off is obvious (Siri/system language changes), so only useful if you're already running an unusual locale anyway.