I just have 2 suggestions, and they are the main reasons behind why I don't use HTML5 full time.
1. The Camera - Make it SAME as flash, or give an option to make it such.
For MM and normal gameplay its fine really, just takes a little getting used to, but for XP/BP it is like a whole new learning curve and still not as good as flash. And since a lot of people play XP only, they would find it to be a good reason to make the switch if camera was made same as flash.
2. Resizing the UI - Add option to scale / move elements of the UI according to your choice, like making the supply bar smaller etc. (Example - PUBG Mobile Customizing controls)
I think on screens of smaller resolutions, the UI takes up a little more space than I would like it to in a battle. Where as on flash, its very slim anyway. Having a slimmed or toned down UI helps in focusing more on the battle, obviously this isn't as big of an issue, as the previous point but still a good-to-have.
If these 2 things, or even the first one was considered, I'd probably switch to HTML5 with no issues.
Oh and also, make F11 work for full screen, or add a fullscreen button when in battle. Only way right now is to go to garage and then press the button.