The only reason people equate shonen with adult storytelling and demographics is because the most popular ones are usually action-heavy and aren’t afraid to show blood or delve into serious topics. Pokémon is halfway there already; while it is true shonen as a genre is, generally speaking, “better written” than Pokémon, a lot of these mature themes and topics can and already have been portrayed in kid-friendly Pokémon. A good and well-developed story doesn’t need any of these either; but I’m of the mind that the more complex and layered a story is, the better it is. Something like that will always be better than something simplistic and safe, provided it’s written well.
The difference is the delivery/execution; which I do agree is the biggest factor holding the anime back from being something more than it is. It’s a structural problem with how the anime is written and until there’s an overhaul in direction Pokémon will probably never reach those insane peaks shonen fans are accustomed to.