Yes, I agree with that. I think it's good that Godot is moving to Vulkan for the future, but sadly support is not great on old or lower end devices. Especially for mobile, the hardware and drivers are not mature, and a lot of non-flagship phones don't even support GLES3, let alone Vulkan. Which is why I am using Godot 3.x and GLES2 right now so the game can be played by the most people.
I terms of Godot 4.0, we may be a year away (or longer) before it comes out, so technology will have advanced. And it's likely that Godot 3.x will be supported and maintained for some period even after 4.0 releases. No one has given an exact timeline, but I would guess at least a year, given that Godot 4.0 will not be complete at launch (missing WebGL and some other features).