Offense, Defense and Utility I agree with, but I find the 18 maximum trees a lot more simplified and easier like it was season 1 again
I am like season 6 a lot more, combining season 6 and second half of season 4 would be the better, while removing all season 5 elements. Red trinket is stronger than before, and there was never a pink trinket.
Season 4's Spirit Stone/Madred's Razors/Quill's Coat options would be good to re add and then they can combine to any enchantment later. Spirit Stone more focused on magic damage and casters, so opening up mage junglers, Madred's Razors for attack damage and basic attackers, and Quill's Coat for tanks; jungle only stats obviously for these starting items and their direct upgrades, stats later for champion combat with enchantments.
Dragon needing a full rework moving away from the season 5 Dragon, I actually made a concept of a Dragon Shop and slaying Dragon grants special currency to enter a different top tab from the shop to get what you want, including immediate temporary bonuses. The permanent bonuses slowly build up based on Dragons taken, with a very tiny respawn on dragons for something to do more often to create less down times of nothing happening; like 40 seconds respawns