Is it really that important?

With the latest generations of main series games having less and less post-game as they follow, it's interesting to reflect how much impact it has in the games's final quality.
It appears Gamefreak has been focusing in developing the minimum for what can be deemed as content after the player beats the Champion, such as a epilogue storyline to tie loose ends, a battle facility for players to challenge the AI, instruments to breed and train Pokémon for online play, League rematches and the classic finish the Dex.

However, perhaps the situation could take a turn and instead, what if all the important content was inserted into the campaign itself?
Having a large number of routes, locations, towns, dungeons, all inside the journey, contributing to non-linear gameplay, where the player could encounter numerous NPCs involved in side stories and optional battles with rewards, such as useful items and rare Pokémon,
All meanwhile the player can opt to make more interactions with characters and play with features related to raising their Pokémon, with all factors aimed for the games's climax in the League.
The direction could aim for a more fulfilling journey gameplay that didn't leave anything to be desired in the end, having the post-game to serve primarily competitive & completionist features.

What do you think? Would you trade post-game for a more fleshed out journey?