Yep! Regrettably the issue I had was getting JS and HTML5 form validation to work nicely together. The issue was that the HTML5 validation was triggering before the onsubmit which was when we were reviewing the entire form for consistency. So even though we played around with it, and in some places used it for "required" it just didn't work out too well with a lot of the ways we were validating forms. I'm sure we could have made it work - turning on and off the HTML5 validation as needed, using an onclick or some other event instead, but it was easier to just let the non-JS version be validated server-side (which we obviously do as well, as any sane dev would).

I am a fan of the HTML5 validation though - offered feedback when they were working on it that I think made it into the spec like interaction of required and hidden elements...

And, I suspect for most of our forms the simple patterns of HTML5 validation would be fine, it's just that sometimes it wasn't, and it was easier to be consistent in how validation worked and looked... So. Chalk it up to laziness. So long as the forms still worked we decided to let it be.