1. You're simply not going to achieve consistency across the board, because even if you dictate this by fiat, your dependencies won't be like this. The issue of the function name being hard to spot is easier to fix with tooling (just tell your editor to color them or make them bold or something). OTOH, it's not so nice to be unable to tell at a glance if the function return type is deduced or not, or what it even is in the first place.

2. It's incredibly rare for it to be required. It's not like 10% of the time, it's more like < 0.1% of the time. Just look at how many functions are in your code and how many of them actually can't be written without a trailing return type. You don't change habits to fit the tiny minority of your code.

3. This is probably the best reason to use it and the most subjective, but still not a particularly compelling argument for doing this everywhere, given how much it diverges from existing practice. And the downside is the scope also includes function parameters, which means people will refer to parameters in the return type much more than warranted, which is decidedly not always a good thing.