>Granted many are not as feature rich, but they'll still be HTML5 compliant.
This is a meaningless statement. HTML5 is a moving target. And on top of that, webpage design has deteriorated to the levels we saw around 2000 again: to be usable, your browser has to mirror the most popular engines well enough that sites work.
Most of the browsers I exampled used popular engines (Blink, webKit, Gecko).
And if you want to get pedantic about HTML5 being a moving target, technically it's not. People often lump the other web front end components (CSS, SVG, EMCAScript, etc) under the HTML5 heading - those components will obviously have their own specification enumerations. Furthermore, a lot of the tertiary technologies that are a moving target are either experimental features / proposed drafts (ie not part of the final specification) or browser specific extensions. Most sites tend to avoid using these without fallback code for non-supporting browsers (demo sites being the obvious exception).
This is a meaningless statement. HTML5 is a moving target. And on top of that, webpage design has deteriorated to the levels we saw around 2000 again: to be usable, your browser has to mirror the most popular engines well enough that sites work.