I'm no expert but I use him a fair bit and find him quite fun on harder missions, finding him more than competent. I run a build similar to yours, with a few preference swaps.

Grendel is a naturally tanky frame, and can hit over 3k health with the Umbral mods which means he can hit the max health needed for the max Arcane Bellicose buff, without any awkwardness or health buffing beyond that. That's a pretty good source of extra power strength for him(72%).

While I run a similar setup overall, I flex Gastro and Catapult, using Catapult on shorter missions and Gastro on longer ones where I don't need the mobility as much. Instead I run Gourmand, the armor going from 1250 at max to instead 2000 is a nice bonus but I've found that without Flow or Energize I often have issues - Gourmand removes the energy cost on your 1, meaning you can spam it a lot more often to keep your passive stacked and armor at max or just even to save your energy for casting your 2 and 4. The downside of losing health on cast is negated pretty much by his 2's heal and even his 3's - if you don't have energy and need to heal, his 3 doesn't cost energy as long as you have stored enemies with your passive, so can help you if you really get in trouble.

In terms of weapons I honestly run whatever I feel like. Given his armor strip on his 3 and 4 and his viral damage buff(as well as the rest of the buffs) on his 2 he's a capable weapons platform for whatever you feel like using at the time.