I haven't played too many games yet unfortunately, but I'm shocked to hear that someone doesn't like the Mehal Sefari. I've found them to be fantastic and have immense staying power, and they are nuts with the built in trigger on the gun while in glory.
Never got to try rail gunners because they are always my opponents first target. They read the card and its a 'nope' moment.
Basotho Cavalry I've found to be adequate for their cost, likely a better summon than anything else.
Probably an unpopular opinion, but I really don't like crow runners, which sucks because I love the models. I always regret taking them and have yet to see them live past turn two. Really great for scoring early points but not worth losing what I consider an overpriced unit in exchange, compared to nearly anything else, they fold like a wet noodle in a blender. Good summon though.
Lord of Steel is really good, and may well be the best objective runner in the game from what I can see.
Completely disagree with OP on Unathi. Sometimes he can be a bit on the boring side, but is still very good, he embodies our faction perfectly with his play style, our units need the staying power he provides in many circumstances because losing a unit for an elite army like ours is so much worse than any other faction. One of my main opponents is Gibbering Hordes and I can safely say that Unathi =/= better Gibbering Hordes. The mechanics are very different, and you can stop Unathi by murdering him, which the Stormsiren is very well suited to facilitating I might add. The Hordes are truly endless...
Okay the Dreadnaught has been pretty crazy for me, but I don't think that's entirely his fault. Every game I have used it, it has been supremely effective because my opponent was totally unequipped and unprepared to deal with it. Either to not having the correct selection of units to hunt titans, not taking those units, or not understanding how to deal with something that can do so much and take so many hits. Now I've seen the argument in the ongoing Rhino thread (haven't had the displeasure of facing any myself) that a player shouldn't have to build their entire list around a single unit, which I do agree with. But we have three potential titans we can take, so I feel that if the opponent doesn't take into account one of the biggest selling points of our faction, its really on them. With Abyssina, you best prepare for titans of some variety.
Engineers are great, I absolutely love them
Those are all the units that I can speak to because those are the only ones I own (guild envoy is pretty swag tho). Nothing to me stands out as particularly overpowered or particularly bad, and I'm sure even the crow runners are *probably* fine, I just need to play them a bit more (their glory side is pretty crazy, but I've yet to get them there)