Even that's unfair, really. They weren't really trying to "deceive", or at least I don't see any potential gains from doing so. The one argument seems to be "they lied to drive sales of bright engrams for silver (real money)". That doesn't make internal sense, though, since those sales would only get driven if users knew they were facing a longer and longer grind, and elected to buy the engrams instead. By not telling customers this was happening, they cut that possibility out. So I can't agree that's a reasonable explanation.
It seems far more likely they wanted to disincentivize "loot cave" type grinding, where you do the same thing over and over (like heroic public events, currently), in favor of mixing things up and doing different stuff. Especially since they stated that XP gains were increased for certain types of content, by this same system; it wasn't just a throttling.
Is that bad messaging to customers, because A> they didn't know this would be happening and B> the game UI reported the full XP but only applied a fraction? Sure. Is this reason to start boiling the tar and getting the bags of feathers ready? Really not. Especially when the conversation basically went;
"Hey, Bungie, it looks like you're throttling XP, see these screenshots? Isn't that kind of fucked up that there's no messaging about what's going on here?"
"Yeah, you're right. That's not working out like we'd hoped, based on your complaints. We're gonna end that right away and see if we can work out something better moving forward."
If that's where it ended, fine, but instead we get;
"OMFG, Bungie is LYING LIARS who are trying to STEAL MONEY by making customers make VOLUNTARY PAYMENTS by NOT TELLING THEM THERE'S REASONS TO MAKE THEM."
Which is nonsense, really, if you sit down for half a minute and think about it.
It's like the lootbox stuff. Don't like lootboxes? 'Kay. Don't buy 'em. They're not functionally different from packs of trading cards, in terms of whether or not they're "gambling" (I'll admit they could be defined that way, but only if that definition is so broad as to be silly in terms of banning stuff that it covers). Lootboxes and microtransactions are everywhere today because customers like them. If you don't, that's fine. Don't buy 'em. Why get bent out of shape if others do? If you're straight-up buying advantages in the game, that I can see as an argument for "bad gameplay", but that just means the game design is bad and I'd recommend not playing it, not that it's some egregious wrong being perpetrated on unfortunate customers. I think more of the average consumer than that.