The Conquest is not F-tier by any stretch. I think it gets a bad rap because people expect it to be something it's not. It's an opportunist, not a slugger, and its not not supposed to be trading shots with capitals but rather with cruisers. It's a cruiser-killer. It outmaneuvers the Dominator, outguns the Eagle/Aurora, and can lay waste to Destroyers. Its shield is a tell-tale sign that it's not supposed to take a lot of hits: not only is it in a limited arc but it has poor efficiency.
A well-built Conquest is like most of the Midline fleet: a really good generalist that gets out-shined by the specialists in their respective niches. I like flying Conquests as a flagship because I don't feel like I lose a lot speed going up from a Cruiser but boy do I gain a lot of firepower. I don't expect it to take on well-built Paragons, Onslaughts or Stations by itself but I know I can take out about anything else.
If it specializes in anything, its sustained firepower. With its superb dissipation and capacity, along with the efficiency of Ballistics, it wins almost all flux wars if armed correctly. I don't think its maximum focused firepower is top-tier but it can sustain it, which is important in its own right.
Odyssey is in about the same boat but it trades some firepower for extra burst speed relative to the Conquest. It can also absorb more damage because its shield efficiency is stellar.