There are cases when P4 is the only choice (large binaries come to mind, and really really big code bases) but it's the kind of thing you shift to because you have to, not because you want to.
Agreed. I use git-p4 for interacting with p4 servers here at work. I love that I can create my commits and make them as granular as I want without having to interact with the server until I'm ready to submit my commits.
Using git-p4 means I don't have to 'p4 edit' my files before I edit them (which really sucks when the p4 server isn't available for any reason), I can simply put off any version control workflows until I'm done with my changes (and slice and dice the changes the way I want with interactive rebase).
Thinking of all the little interactions I do with git which a) aren't possible with p4 or if they were b) would involve talking to the server every step of the way makes me cringe. But then out of necessity, p4 developers probably aren't creating such fine-grained commits like I like to do (and indeed isn't even possible without a lot of fore-planning with p4), so they wouldn't notice the speed impact.
When looking at an actual example of the latter [1], you will see that they are heavily optimizing against contention on the central database by limiting the size of database operations. If you want to do something that would require a longer database query: Enjoy your client side error message about implementation details you never wanted to know about.
Unfortunately I did not mean to. I would agree with you that binaries are the 95% use case for P4. I think most developers typically wouldn't want to check many or any binaries in (maybe the odd icon or other small, slowly-changing asset, in which case git is adequate), but game developers and people with other binary stuff (e.g. circuit designs) will have large, changing binaries.
However really big (GB-scale) repos can be painful in git. This is why google gritted their teeth and used P4 until they outgrew it too. That's what I meant by "really really big" -- something of the scale that most of us will (hopefully) never see.