You don’t lose any language server features, you just access them slightly differently. Each function in io-ts, zod, and other TS libraries like them) are type guards, and have companion utility types to extract the static types from their runtime definitions (with `typeof`). I’m certain that io-ts handles generics (I’ve used it to do so), albeit again slightly differently, in that you need to define them as generic type guards.

I think the clamor for runtime type checking in TS is partly because type guards and their benefits could be better explained at the language level, and partly that libraries implementing them effectively are mostly aimed at users who already understand those benefits.

You really don’t want pervasive runtime type checking, except at API boundaries where data is untyped (i.e. the appropriate type is `unknown`). Type guards are exactly designed for that use case. For other cases where the types are well known, runtime type checking is needlessly expensive and redundant.