>urrently rendering HTML5 and its transformations is a complex subject, without competition we don't know if there are better ways to accomplish this task.
Why, did anyone told you that the various engines differ in how the go about those in any real way that matters?
It's mostly duplicated code and similar approaches.
And even if it wasn't you can have different approaches in the ONE AND SAME codebase easily. Test alternatives out and see what works better. It's even easier when everybody is using the same engine, because you don't have to also implement EVERYTHING else yourself in order to implement one thing differently.