You aren't missing much, I watched the first half and it's just streamers being whiny streamers for attention, as they always are.
It still is fun as fuck to play. At the end of the day, that's the goal. But some decisions are just shitty on the gameplay and systems.
Do you play any arpgs at all in the history of ever? The season mechanic spawns a bunch of mobs that drop loot and then you get reward chests for a touch more loot. Is it crazy innovative? Nope. Is it functionally identical to every mechanic in every arpg? Yep. Poe2 league "stand at this tower and kill mobs. Some towers are short, some are longer" Wow such innovation. One of the "favorites" leagues of poe? "Run through this map for 3 minutes and hope it gives you lots of wisps, then go do your actual map and you get extra items!!1!" Wow, so amazing, such innovation. etc. etc.
Superior Lair Keys replaced Belial fragments, basically Belial drops them when he spawns randomly when doing lair bosses, and you can get some rarely from Greater Lair bosses too and I think any "key" source although a lot more rare than others. And yeah Greater Keys still drop from normal lair bosses amongst other things, sounds like bad RNG or maybe low torment? It's best to wait a bit before running lair bosses, like until T6 or T8 or so.