Probably true to some degree but Bungie engines aren't a shining example of lean and mean. They didn't aim for 60fps and that's all there is to it.
This is basically it. I mean, if you want 60 fps, then you have to work to achieve it. In the history of developers talking about, and implementing higher framerates into their console games, they come at it with a development paradigm from the start where they actually *want* it. It's a desired thing.
Sometimes, they want it, and they can't get it and it's not for lack of trying (Uncharted 4).
But they are open and honest about the reality of it. That they tried, and they didn't get it, and the reasons are complex but they do their best to explain it as a series of choices.
When you think about games like Rage, for example, the design philosophy of the game was "Oh shit, this is tanking the framerate, this thing has to go", so it fed back to the system and then got cut. And I mean, there are technological work arounds to these things -- dynamic resolution as an example. Yes, you lose some things, but in multiplayer, for example, it's a more closed off space -- there are inherant limitations to it. The public space doesn't have 16 people running around, or whatever. You can certainly make a case for D2 in its PvE not achieving it, and I think that's fair, but I am struggling to see their excuses for PvP not being 60 fps as anything other than "Hey, we didn't want it."
And if you don't want it, okay, be honest about that and that can become the core topic. But don't act like it was some not achievable thing by the hardware's standards.
edit: As regards cpu bottleneck, I mean, there's a wealth of more 'rich physics' going on in a patrol than is likely to be seen in a MP match. Consider what they talked about: vehicles, AI, lots of enemy units -- all physical objects -- in addition to the players (the max having gone UP to a much larger number). So, they're explaining away the limitation in terms of the PvE experience, which is fine, but then you're saying that in the world of PvP (that is not likely to have AI units, vehicles, all of that) being included into their physics simulation, and a max of 8 players (lowered from the total of 16 or something in public playspaces) and you're telling me that all holds perfectly steady at 30, but on a move to MP, where we could afford reasonably to drop the quality and even implement dynamic resolution, that that is completely out of the question. What they have reasonably explained imo is why they can't have it in PvE, and I accept that, but I don't accept in a much smaller location, with fewer NPCs (0), no vehicles, just a lot less in general going on, that suddenly the lack of dedicated servers (something they are basically saying is out without much other reason) is the real gotcha. That doesn't add up to my admittedly stupid brain.