I agree there is plenty of space for the PL to grow, the issue is really how much.
In some ways, the question is why the PL, despite having such a large global audience, makes so much less money from its broadcast rights. The implication from people backing the Boehly perspective is that they're just not doing a good enough job monetizing the product. But not only does the owner of a big club actually have little control over that, there are also a number of factors that suggest that monetization isn't really the most important issue.
-The PL has a big global audience but a huge part of that audience has relatively little disposal income, at least vis-a-vis the US TV audience, and particularly isn't a major target demographic for the most lucrative of advertisers like car companies.
-Compared to the NFL, the structure of football offers very few advertising opportunities. The average NFL game includes 63 minutes of commercials, a totally insane number. Moreover, they come in short spurts so the audience often keeps their eyes glued to the TV/stream because they don't want to miss the next play. With a football match, if you just tune in right before kickoff and turn it off at the end, there are generally a couple commercial breaks right after the first half ends and right before the second half begins and that's a time when half the audience is taking a piss, having a smoke, or just obliviously chatting with somebody else in the pub.
-Americans will basically watch any NFL game, even matchups between terrible teams put up huge audience numbers on national broadcasts. While the same may be true among a certain segment of PL diehards in the UK, the global audience of the PL just isn't interested in Bournemouth v. Forest at all. There are more PL games than NFL games, but the vast majority of PL matches aren't actually very big draws for the global audience. People in China may not care about NFL games between terrible teams either, but its the 330m strong US domestic audience - which does care and will watch - that drives the NFL broadcast revenues.