Taking a quick look at the Top Mods of all time for Valheim and the proof is in the pudding. Sure there's some neat mods that add content to the game like Epic Loot with magic items and enchanting, but the majority of them are QoL mods that just make the game more enjoyable to play.
Mods that could very easily be implemented into the base game by the developers but simply are not like Pulling resources from containers for crafting, Customizable portal restrictions, a better UI, grid based planting, among other things.

These shouldn't be things that you have to mod in, but they are simply because the base game does not receive worthwhile content updates at a timely pace.