I get it - Seasons is a way to experiment. It’s also a way to release unique content that you want people to pay $ for. That’s fine. But take a cue from games like Magic the Gathering. They certainly make $$$ from their regular seasons. But if you could only use the current season in a Tournament and then after 3 months your cards were useless nobody would buy or play. So your new Season cards are good for 2 (now 3) years which is about 6 - 9 seasons before they get retired from general tourny format.
I think this pattern would work well with Diablo Seasons as well. I think there would be less player resistance to Seasons and new characters if each season were part of a larger set, and your new characters were playable throughout the set. So a new character in Season 1 can be used in Seasons 2 & 3 also, but Season 4 starts a new Set or Block of seasons which necessitates a new character. Within a Block, each Season may have its own unique mechanics, but those mechanics would tie together thematically within the Block, and the unique items would develop synergies together. It may require a bit more planning ahead, but I think this is a compromise that would allow the developers creative flexibility while also not requiring everybody to start over every 2-3 months. It would also still support new players because they would know that each Block will start everyone over. What do you think?