Yeah those champs snowball too for sure. But i feel Karma as a range mage, with sustain and escape (not mobility escape), snowballs harder or at least feels harder/quicker. Lux, being one of the only other range mages as you pointed takes well into 100CS plus 1-2 kills before you feel her pain compared and has way more counters compared. And those you mentioned as counters to Karma don't even really play in her lane and that is the problem except Yas.
Overall her entire kit is much better and stronger now, but i think a little too strong. Just look at the math on her empowered Q alone compared to Sona Q+passive. It is night and day.
I really don't want to continue arguing really because it is just stone cold fact she is one of the strongest supports in the right hands but of course the numbers won't show it unless you look at why she is being beat most times. That reason is sustain supports. Sustain seem to be the real reason she is not looking as powerful atm. As the later it gets, like all champs, the stronger they become, this isn't more prevalent with any other in supp role than it is with Karma. Games that go 25+ mins up to 40 min mark show how strong she can be, and this is because this is when she can finally punish a sustain support team by putting out more than they can input for heal/sustain. Of course after that she gets weaker as all mages do. But it is sustain supps which is why she is SO DAMN LOW on winrate, and this could be because in higher ELO sustain helps so much more than damage when the skill level goes up with your allies. Less engages, less chance for ganks and just more time for the sustain to let his/her ADC out farm.
If you look, most of her loses are from sustain supps vs'ing her. Sona, Soraka and janna, all high lose rate supps for her to vs. Then you have displacement and protection up there to as high loss rate supps.
This also looks bad as the player base from 1-15 games played for Karma is so damn high it isn't funny, which alters the winrate a huge amount which means a lot of people are picking her up in high ELO games and not maining her. Which muddies up the winrate massively as she still takes a good amount of skill and time to perfect and time her abilities for supp role (where mid you have more free range to test earlier on) I would say to know exactly how to Karma Supp you would need 30 games minimum so if you were to shave those games off that rate you would see easily a 52% winrate over what we see there.
Right now sustain supps are just in the best spot. Since the Mik and Ardent buffs they have seen a huge leap in popularity and winrate comes with it. Once they finally mess with healing once more (Riot seem to hate healing) we will see Karma rise up for sure.