I don't see how this would have prevented this problem. The issue was not that regular expressions were "too hard" for the lastpass team, but that URLs are hard

I don't see how this would have prevented this problem. The issue was not that regular expressions were "too hard" for the lastpass team, but that URLs are hard to parse correctly. To put it another way, if you don't know how to parse a URL correctly, you'll probably write an incorrect parser no matter what parsing tool you use. That's why you generally shouldn't write parsers for URLs.