Inferred types are really great, but I feel they do not scale. Inside a method/function? Generally fine, but the signature, including the return type, had better be explicit.

Also, I think there was some performance issue with too much inference? Could be wrong, could also be fixed.

This. As soon as you need to use the type in another function (e.g. function parameter), you'll discover that it's better to just write it out.

They do scale, but explicit types have two bonuses in my eyes:

1. can be read without a compiler, useful when reading PRs

2. They make the compiler work less, it's easier to check than infer