The number of times I've gotten two or even three critical failures/misses in a row is mind boggling. That said I've watched the NPCs do it as well, so there is a semblance of fairness. You're right that the statistics feel off, but as is always the case, our minds are going to focus on these outliers without recalling all the many times the dice fell right in line with expectations.

I do swear that a 50% chance to hit with a Sacred Flame consistently feels more like a 15% chance.

Karmic dice are not random. They try to reduce your number of streaks of successes and failures, so if you have highly competent characters they'll sabotage you more than they actually help. That's not how real dice behave.

I never play with karmic dice.

Look, somebody did the math.

They are definitely modifying the dice rolls in some way in tactician and honor modes. You can see it in things like ability checks. Normally you'll have a chance to roll well for any roll even if you don't have proficiency in the skill, for example a 15 CHA dialog check and you have 8 CHA, if you roll a 16+ you'll pass it. On tactician and honor mode if you don't have proficiency you'll struggle to pass the check, all your rolls will be under 5 usually. I've burned 4 inspirations with advantage before and watched 8 dice rolls under 5 for a skill check I wasn't proficient in multiple times in a run. I just ignore it now since it is what it is but I really wish the difficulty wasn't rigged like that. It'd be great to have a fair but brutal mode.