CapnZapp
Legend
Why even have this discussion?Collecting magic items in dungeons is not common. Adventurers make up maybe 1% of the population of the world? The number of magic items in a given setting compared to the population of the setting is very, very small.
The rarity of magic items is in relation to other magic items. It has nothing to do with how common they are in the world itself.
There is no objective stipulation of how rare or common magic items are, and there never have been. No matter of hoaky statistics hurling is going to change that.
It's all up to
a) your DM
b) the adventure
c) the campaign world
The only way to gain a practical feel for how common or uncommon magic items are is to look at a representative scenario for the campaign you're playing in.
Thus the answer is both "common" and "not common" and none of them are more right than the other. For you Ibrantheloth, the answer might be "not common". But it's a folly to try to impose your answer on Yunru, who might be playing Storm King's Thunder, set in the Forgotten Realms.