ud is in an awful state balance wise, their exotic and legendary runes are equal to common and uncommon from other factions.
Which part ? Do you believe themes in ud are as strong as themes from other factions ? Imps, spiders, fire amp, arrow eater, goblins, are all pretty sub-par as far as themes go. Ud used to have massive strength as far as their bonus goes, however most units from new expansions start off at 13-14 damage or have an ability to significantly increase damage output. Also any sort of cc still nukes ud. Plus the whole, not having any ranged units doesn't help either. Especially considering some other factions have ranged units that can smack for 14+ damage.
Themes, yes, they're quite weak aside from Minotaurs and Spiders. Upcoming patch should fix some of that though. As a whole UD has lackluster options in terms of CC, but UD meta is still, in spite of all that, one of the strongest decks in the meta.
Spiders are still kinda of weak as well, they have a few tricks, but mostly the stronger damage output spiders are all 2x2 units which messes with mobility and more spaces to take damage from ranged. I'm not even sure what a ud meta looks like other than some angels, and cheap stuff. I've watched 6 games today of ud players, they were all steam rolled pretty easily. Just seems the damage of other factions has caught up to the ud bonus, but ud still doesn't have great ranged options, or cleanse, so they fall behind. Ud has a ton of sub-optimal runes with double nora/hp ratio. Hopefully it's fixed though like you said. Also, building a fire bg, when your units have fire eater, but also lava walker seems counter intuitive. Maybe fire needs more fire acolyte, and less fire eater ?
Fire is also a very strong theme in UD. High up there, along with minotaurs. UD meta isn't really angels and cheap stuff. The problem with it is that it's a bit too predictable and one-sided. Limited options of high efficiency units, which leads to bad matchups (vs. SP in general due to spell resistance, vs. things like constructs, some ST themes, it becomes near unbeatable.) However, that doesn't significantly diminish its powerhouse. I've had a consistent 85-90% WR with Minos and Meta.
I think in terms of strength, we are both using different parameters. Ud is the weakest faction in my opinion, that's not to say good players like yourself can't get wins, or the average player like myself can't squeeze out a win here and there. I believe it is for the reason you listed, and the reasons I listed, poor efficiency, not enough bang for the buck champ wise, very predictable. Also I believe the damage of other factions is catching up to the damage of ud, but ud damage doesn't have a whole lot of champs with burst damage so to speak, not that ud needs it, more that other factions shouldn't be hitting for 20 damage in one hit. Ud doesn't have really many theme tying spells or abilities to boost stats either. Very few defensive spells, no theme spells, equips, relics, other than like firelight gem and the couple bad spider spells. no cleanse no champ saving spells not a lot of healing poor ranged champs not very thematic- not many theme spells, equips, relics for themes inefficient champs- especially ranged champs, looking at the regular imp makes me wanna cry. 66 nora for 3-4 range, and 32 hp. yikes man relying on hekatin bloodguards summon for ranged damage lol ud wants to rely on anti ranged- but actually have few inexpensive arrow eater champs other than pincushion and the one spider overall the biggest issue- Inefficient, costly, and surprisingly squishy. Looking at the poor ireguards, which honestly a simple fix for the ireguards would be to give them the ability that blocks enemy spells, and give them faithless or something. For 90 nora, other factions 90 nora units have like 60 hp and are monster stats wise and ability wise. Hopefully this next patch fixes some of that =)
I've been advocating for a big UD revamp since 2016, so I agree with your sentiment and to an extent your assessment. That being said, UD still remains one of the strongest factions, in spite of all its flaws. It still has the strongest early game potential, smoothest kills and trade value, some of the best spells in the game. UD was never meant to be ranged. Range buffs in this patch is a soft compromise. The most I can agree with is the thematic issue, but that, I think, has been the bane of UD as part of a sort of atavism that guided the logic behind making everything race: demon back when Demon Shield was meta. But don't worry, this patch should be very good for UD. We're finally getting some decent relics and equips, along with some spell changes. Further patches will only move more in that direction.
I might disagree with strongest early game now, given recent buffs to other factions, and ud damage still lacking burst damage in most areas compared to other factions early deploys. What do you mean by smoothest kills, like simple kills, or what ? Ud spell set really does feel unique and I quite enjoy it actually, anytime I want to mess around I play ud because the spells are funky. Ud wasn't meant to be ranged, I know this, but ud's lack of range, and their anti-range units being very expensive, really leaves a lot to be desired. Also given other factions ranged units, now smacking for a damage equal to the ireguards, it's tough to say they don't need some sort of ranged. Me personally, i'd like to see a little more alternate ranged attacks spread throughout, throw shield, throw axe etc. Really looking forward to the relics and equips