I have never been a big fan of MXML because of the huge dependency on the framework and UI components etc.
But that's exactly the pros and cons, if you use MXML and in this case Apache Royale
you have to accept to delegate to it all the UI and render thing and go with its way of doing things.
It should be possible to use Apache Royale in a pure AS3 context but then
you will also have to build anything UI by hand which could be quite daunting for an HTML5 target.
Maybe go on the Apache Royale mailing list and ask them or do some tests yourself
with simple stuff.
It really depends what kind of app you plan to do with HTML5,
if it is quite advanced you might want to do it in Angular, Apache Royale, etc.
for the components part
If it's quite basic, eg. you could do it by hand with a bit of jquery,
then anything would work I guess.