I mean... most Isekai is shounen? Shounen just means it's targeted at young men. There's some solid, complex isekai concepts, but, overall, it's a current trend with a lot of cheap cash-ins. The same way the YA market in America had that big dystopia boom that included both some amazing, thought provoking stories, and a bunch of cheap cash ins.
I think a better phrasing might be "which is more popular, battle series or isekai". I'd say very few of the top series are isekai, but there's more new isekai than anything else? They're kinda like paperback romances. Plenty of people enjoy them, and they may sell well, but very few people are declaring 'Passionate Nights with the Duke' as their favorite book. The copy-paste isekai tends to target a younger audience, so has more people who'll insist 'The Useless Blacksmith has the Best Stats and the Biggest Harem' is a masterpiece, but not many.
Though, again, not all Isekai is wish fulfillment fluff, and I imagine some will go down with other great shonen. Battle shounen is literally the most popular manga genre, so the idea that HxH and Jojo are lost an underappreciated is nothing to worry about. Honestly, as we get more older manga readers, I'd love to see more Seinen and Josei getting big in the US.
But my personal fav manga is a reverse-Isekai Josei, so I'm highly biased.