Here's some of the highlights for different years of Cats that I posted in another thread.
2012 (agree it was a train wreck)
2013 Limiteds got short coolers and painted tunnels and rails cutting way down on snow and ice buildup.
2014 had 26 improvements over the 2013 scattered throughout the sled. Rode better than it's predecessors and truely was IMO what the 2012 should have been.
2016 got new suspension geometry front and rear, all new clutches, stronger chain case components, new skis, and a 3" track option. Rode better than its predecessors. This was as good of an overhaul as a XP to a XM IMO.
2017 Mountain Cat got revised driveshaft location and narrower running boards/belly pan, lighter tunnel. Yamaha turbo powerplant. Rumor is should have been new ctec motor too, but changed piston vendors. Polaris would have hyped it, sent it, and dealt with the fallout.
2018 new ctec motor, new primary clutch, new plastic, dropped a little weight. Between 2017 and 2018 change to Ascender was another XP to XM type update.
2019 Alpha rail and track option with 10" wheels to free up HP and new skis.
2021 equivalent of FOX IQS suspension setup available from the factory.
2022 Finally sealed up the intake!!! (haha) New lighter, narrower primary clutch.
After riding a twin rail Acender with Elevate kit that is what I would get next for best all around platform. Alpha is great in deep snow and easy to spin around, but not as stable as I would like in lower snow situations where hard, old tracks and holes are underneath.