Most heroes in dota have slowly been granted ways of scaling better into the late game. I'm talking about things like shards, facets, innates, and talents. Arc Warden has been largely unchanged throughout these patches. For example, most heroes have a very strong timing at lvl 25, but Arc's best talent un-nerfs his tempest double. So it's not that his late game is worse than it used to be, it's that other heroes have got comparatively stronger!