Google's John Mueller had to say on Twitter again that Google does not penalize sites using old school HTML, like old table designs or invalid HTML. He said "no, we don't penalize sites that use old-school (or invalid, table-designs, etc) HTML."
Here is the tweet:
1 - no, we don't penalize sites that use old-school (or invalid, table-designs, etc) HTML. 2 - I'm not sure what you mean with "boilerplater sites".
— 🍌 John 🍌 (@JohnMu) November 18, 2019
Google has been saying invalid HTML doesn't hurt you in terms of Google rankings. Most of the web is broken and invalid and Google needs to figure out how to crawl, render, index and rank it anyway.
So don't you worry too much about that from a ranking perspective. If things are broken on your web site, that might not be good for your users. But Google should be able to figure it out. This does not count broken schema or markup, be careful with that.
Forum discussion at Twitter.