Kill the longevity how? If you are legitimately solo-leveling an alt in the Season, you can get to WT4 in a weekend. If you get power leveled, you can get there in a matter of hours. At most, you are cutting down like 12 hours of gameplay in a Season - only for subsequent alts. You have to put the work in initially to get there for every Season.
You do not have to use the token and can play your Alt from LVL 1 if you wanted. All this does is promote players to try out Alt classes within the Season.
To your point about Loadouts, it absolutely should be in the game. I should be able to maintain multiple Loadout profiles so if I started off playing as HoTA Barbarian but found it boring and wanted to play Double-Swing, I could. Alternatively, if I found Aspects and gear that leant itself more toward Upheaval with a Hellhammer, I can swap to that and play in Season.