Unnecessary elaboration about not being assignable to type parameters

[DanielRosenwasser]

async function foo<T>(x: T): Promise<T> {
 let yaddable = await getXOrYadda(x);
 return yaddable;
}

interface Yadda {
 stuff: string,
 things: string,
}

declare function getXOrYadda<T>(x: T): T | Yadda;

Here, you'll get an error like

Type 'T | Yadda' is not assignable to type 'T'.
 'T' could be instantiated with an arbitrary type which could be unrelated to 'T | Yadda'.
 Type 'Yadda' is not assignable to type 'T'.
 'T' could be instantiated with an arbitrary type which could be unrelated to 'Yadda'.

Proposed

Either

Type 'T | Yadda' is not assignable to type 'T'.
 Type 'Yadda' is not assignable to type 'T'.
 'T' could be instantiated with an arbitrary type which could be unrelated to 'Yadda'.

or

Type 'T | Yadda' is not assignable to type 'T'.
 'T' could be instantiated with an arbitrary type which could be unrelated to 'T | Yadda'.

[jonhue]

I created a pull request that makes the proposed change (#42952) but had one small question about the behavior in scenarios related to the one discussed here.