You don't need to be a top 10-20 WC player to enjoy massive benefits from horde razing that far outstrip PUs, however. If our basis for something being overpowered is "how much of an advantage does this confer relative to alternative actions", it's not even clear that PUs are consistently beneficial. Getting a major or two at an AE discount is broadly good. Getting smaller nations that eat up relation slots for 50 years unless you luck into inheriting can actually be detrimental.
1.31 arguably buffed diplovassaling more than PUs due to the ability to lower opinion/get OPMs to join wars more quickly/easily to feed them then diplovassal. Not only does this cost way fewer favors than PUs, it also costs 0 AE, allows you to benefit from the annexed land decades sooner, and isn't constrained to one religious group.
For something to be "overpowered", it must outperform alternative uses for the same resources/constraints. I don't see that being demonstrated with place relative on throne --> PU with any consistency.
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