I have an exact twin to that Grimm, at +8 with the same build.
I fight almost exclusively 4K+ defense teams that hit hard — I need him to kill things. 
I’ve gone Attack build because I’m emphasizing the existing strengths of each hero using the Talent Grid, rather than trying to “fix” their shortcomings.
Going the attack-as-first-priority route picks up only 36 less defense and 108 less health than always prioritizing those would.
By +20, a full Attack build Grimm will pick up 69 defense and 107 HP in addition to 111 attack. A full Defensive build Grimm will pick up only 36 attack.
Your build is presumably even less of a difference than the extreme version if you chose attack at any of the path choices instead of always maximizing both Defense and HP.
I actually see the full Attack build as a fairly balanced approach — it adds substantively to Attack, Defense and HP.
And while the possible extra 36 Defense/108 HP could help survivability in some cases, I see the 75 increase in attack — nearly 10% of his base — as a worthwhile tradeoff for that.
EDIT: oh, also, full Attack build makes his abs even more rippling (cross linking for future research reference)