Its a metroidvania, it's meant to be completed, the godmaster content was not the best, or rather it did add good stuff and boss rushes are a good way for player to test their mastery of the game and re-fight old bosses, but it also should have given a concrete reward like a charm notch for doing something like clearing the first 3 pantheons.
Allow me to parrot once more what was the most criticized issue there: pantheon 5 was shit and team cherry's greatest mistake, mainly due to its lenght and order: there's a reason games like Kirby and megaman don't gives you more than 15 bosses to fight and either randomizes or let you choose which enemy to fight next, most of the attempts I did failed at the second last stretch (markoth + zote + failed champion) rather than the Moth and having to spend another 30 minutes just in order to get back there is a pain in the ass. I adore the ending it gives you but it's kind of sketchy and poorly explained even to me.
I did unlock the weathered mask, but it didn't felt like a particualrly fun nor painful experience, after a while it just felt boring, having to get all the way up to markoth+zote+champion with limited DPS just to die like fucking retard.