Most people don't have much use for metal (the one exception I found so far is a player that just spams repair all the time, which almost no one else does)

Its even worse in the mobile version where candies don't exist (and thus metal for relationship points). Some people have like, 300k+ metal over there.

I personally am using my metal only slightly slower than I'm gaining it myself though. I guess being in the top 0-1.999% every PoC week for candies (and having the tanks to use those candies on) seems to be the equalization point.