Don't get me invovled in your rants. The similarities could very well be a deliberate act on the writers parts to see how people react to it, and judge things.
Want to talk about what abilities they should have? Sure, lets do it. Want to talk about the themes behind each one
as presented in the pdf? That's awesome. You don't need to know anything about the lore beyond what's presented in the pdf; that's all you need to talk about. Is spy versus criminal too close of concepts? That's entirely in the article and something we can talk about. I'm tired of people just complaining. So, lets get something constructive to talk about and maybe put on the survey in a month about what would be interesting or compelling to see.
Yes, the Glasya and Dispater ones are too similiar. Lets move on from that and talk about ones that actually are different and rather interseting instead of just complaining about one.
Zariel is a tiefling paladin subrace. That's kinda interesting, and unexpected. Think about it - you're getting searing smite and branding smite. You can go BARD or BLADE'LOCK with those spells now, not just paladin. Think about how that could be done. That's a pretty different style tiefling. Fallen angel style.
Levistus in a Con/Cha based subrace. Lets look at him a tic. Ray of frost, Armor of Agathys, Darkness. Definitely a cold-based character, and stats possibly resonate with the Spike Devil feat we saw before. The cantrip lends itself to a more spellcaster than grappler, but if we do go grappler, Armor does work with it. Could be an interesting combo. Honestly, I'd love to see a barbarian style tiefling; while no strength here, we could do berzerker and its intimidation ability with CHA, and the Con boost for some higher AC... well, probably not going to happen. Eventually, we will see a cold-themed sorcerer, if only for the winter-fae theme that was so popular in 4e, and this will resonate well there. I want to like an ice-mage, but the spells just aren't there. Might get white dragon sorcerer to just work barely, iirc, but Armor of Agyths doesn't work with sorcerer spell slots / metamagic. It would almost have to be a warlock again, in which case we'd want to get away from Ray of Frost. Issues, issues. How to fix, and in what way to go?
Fierna has lots of charming spells under her belt, which would be awesome for a lore bard or enchanter-style sorcerer. Not a fan of the +WIS, but it lends itself to being good at perception and reading emotions, so I guess it fits? I wouldn't put a WIS class like cleric or ranger or druid here, but definitely there are other options here. Suggestion and Charm Person are always handy magics to have, and I actually have found use for Friend in a lot of situations, especially if one has disguises.
Now, Mammon. This is.. a problematic one. INT, mage hand, floating disk, arcane lock. Its like it wants to be a wizard, but has rather weak spells to do so. Tenser's disk is handy every once in a while, and arcane lock is... well, I've never seen it actually used by a PC ever. Always NPCs. The spells just don't come up often enough. Definitely not my favorite. There's supposed to be this looting theme, but but we don't really have a class that really resonates with this theme either other than rogue, but all the wrong stats for rogue. And we have a criminal race already (Glasya again).
Dispater. Spies and infiltrators... getting thaumaturgy. Just... no. That's a spell completely at odds with being a spy or infiltrator! Does not fit.
How about trading in the Infernal Legacy trait for something from the cults? Imagine, instead of spells, Dispater tieflings got Infernal Insight. Mammon's spells are kinda lame, so imagine Grasping Hands as an ability instead? Some of these cult abilities are pretty bad ass, and I'm sure that I wouldn't mind seeing a number of them in the hands of a PC somehow, and racial benefits seem to fit perfectly. Would that work? Are there any cult abilities that won't work for a PC type?
Actually, the more I think about it, the more I like the idea. Fiendish boons could be Infernal, could be demonic, and are all interesting.