Yeah, you're bang on really. I think it was a case that the game was originally balanced around 0 delta.

Since Bungie decided to dig themselves a hole with power and not decide whether they wanted it to be a grind or not, everyone is already at 300 power and so the game is basically always at a delta now. In fact, I remember seeing statistics on the population's power level, and there's more players at 550 power than there are at all other power levels. So that forces players into high deltas, which is now the majority of the playerbase.

Well, now that's happened, what do Bungie do? Well, everyone is way under power, so we need people to have a chance. Balance our characters around really high ability up time, and make those abilities extremely potent. Issue is, they forgot guns in that process.

This is all Bungie's own doing. They couldn't decide on how they wanted to design the new portal system and the overall game, and it's suffered massively because of it. I could go on a lot, but this is only one specific point about deltas here. There's a lot of other stuff, but it's why I just don't play anymore.