Celek and Ertz both have good all around games. Both can "run, block, catch". Its true that they both lean a bit better in one area, but Graham is the worst blocking TE I have ever seen and Mercedes is no longer a threat to do anything other than block (and as I said, a T lined up at TE is the same).
The 2 examples of TE you mentioned MM used well were catch only, no blocking TEs. Finley was a try hard bad blocker at least. And again, that is why I said signing Graham was probably a good move for us (and trading an all pro center and a 1st was a horrible move for Seattle.)