Ditto.I solo because I never get a chance to do anything in a group. If I'm a rogue, everyone just runs through the trap anyway and just chugs 10 pots after. If I'm a healer, everyone can self heal. If I'm a tank, the speed 30 9th lifer is already 7 rooms ahead of you. If I'm a mage, I get to buff at the start, after that mobs die so quickly 60% of my spells are wasted.
All the barrels are intact at the end of the quest. That's an anathema to me. Optionals are skipped. extras missed, nobody talks in chat. Only a "hello" at the start of the dungeon and "ty 4 grp" at the end.
When I solo, every barrel is smashed, every optional (thats possible to do depending on build) is done. I can cast spells, I can hit stuff. I can spend more than 3 milliseconds at a chest seeing if the item I looted is ok for my build...I can spend time making room for loot if my backpack is full. I can backtrack and use shrines I missed. I can plan. I can make time to get a cuppa mid dungeon.
I group when I need to if I need quick xp but I really do not enjoy it one bit. Every now and then you luck out and get a nice n slow group. Or I can spend 2 nights a week grouping with friends (which I do).