Earlier quoted context omitted.
Parsing text can be hardly parallelized. Overall it will increase the price of your phone so it can show that webpage fast enough, which will be a cost of both CPU and battery. I have a shitty bi core smartphone, and it really doesn't like webpages. When you look at the source of a page, there is no justification for all of this, unless you like complexity. I did not want to talk about HTML on smartphones, since it a…
Are you sure that parsing HTML is the step that is the biggest issue for your phone, and not e.g. rendering or JS execution? (It's certainly possible, parsing HTML with bad parsers or pathological content can take surprisingly long, but it's generally the last thing I'd expect as a reason for a browser to be slow)
I think it's part of the whole thing, HTML is too permissive, and it also will make rendering slower. If HTML was better defined from the ground up, rendering would also be faster. The sites I visited were not really JS intensive. JS is also a problem for webpages.
Anyway I hate HTML/CSS/JS in general for all those reasons. Parsing text is already painful, why do it each time you visit a webpage?