I don't play any gen 7 games. But I know that in Emerald, your Pokemon are often under-leveled when you battle gym leaders or Elite 4 members, so your best moves often 2HKO or 3HKO them. Attack-raising moves like swords dance turns many of them into OHKOs, and it lets you do stuff like sweeping a team of level 50 Pokemon using one level 46 Pokemon. Do strategies like this not work in gen 7?
But if the TM is easy to find then that's probably a good reason to evolve earlier.