The real power creep, in DF, is crafted items, in which every M+16 or higher gives a shard, that when you combine 10 of them together, you can use it to craft a 418 item.
M+ drops are scaling higher this season/xpac (up to 405), but not better than 2/3s of the heroic raid (402 to 411). They overtuned some of the raid items (trinkets, a couple rings, a staff for Evokers, and a Bow for hunters) to where the heroic level item is better than the M+20 weekly loot box items for those slots (421). In the case of the hunter bow, before the nerf (2 months into the raid), the raid finder bow (385) was, supposedly, as good as a 421 bow from the weekly box.
In BFA and Shadowlands, as far as I remember, the M+ gear didn't scale as high, so heroic gear was always better than the drops, but not better than the weekly box. The box was slow enough, as to not power creep a heroic raid that badly.