Henry wants it

You can check some posts and comments from Nogitsune (just enter his nickname in the search bar here and then check his comment/thread history on his profile). You might be able to find some insight about Henry in his comments, because he's using a +10 Henry. From what I remember, he went all-in on def/res and special triggers. If I recall correctly, he was using an owltome + glacies or ignis with special spiral or something like that.

Henry is really bad. There are much, much better characters you could +10. He is really slow, so he gets doubled all the time. He has good def and res by gen 1 mage standards, but with 32 def he still takes damage from just about all sword users and gets doubled. Being a tank, he really needs close counter which means you can't put anything in his A slot that boosts his stats.

If you really want to, you can +10 him and make him a good unit. You will be unique and prove a point, but he will not be very expensive to build and still not be as good as some of the much more powerful units like Lilina or much more versatile units like Caeda.