This is mostly just out of curiosity 
but what is the smallest group you’ve (successfully) run a dungeon with? I know AC can pretty regularly be done with 1-3 people, but a couple friends and I just tried TA last night (up and forward/forward, didn’t get to forward/up) and it was surprisingly successful for us! Kinda makes us want to take on the challenge of completing more dungeons with smaller groups. 
I hereby summon Weth to this thread.
The Weth call: “This dungeon/boss is impossible!” That should get his attention.
That being said, dungeons are more about your personal skill and mastery than about gear. Sure gear helps – it either enhances your strengths or allows you the opportunity to mess up a bit without so much punishment. There are some encounters that can be a bit of a gear check, but overall it’s more about your personal skill. Solo is possible in certain paths – however some of them have required numbers mechanics: Like CoF path 3 where you need to light 3 braziers at once. Those may have a pre-req party count.
