There is definitely bandwidth as it uses DSC, without DSC then yes absolutely it wouldn't be enough. They have not lied on the hardware side, it is absolutely getting the full panel resolution but the problem is much further back in the process, not at all like BSB.
The actual result sent to the headset will be that 3560x3560@90hz. The render resolution you pick is handled earlier in the process, the issue shiftall has done with this headset is purely in software that they are actually downscaling your chosen render resolution to 3560x3560 THEN applying their barrel distortion etc, this means a lot of detail is lost because ultimately you are meant to render HIGHER than your panel and apply the corrections then send it. At the moment the render resolution chosen in steamVR is essentially worthless.
The good news is this is a software issue or choice, it is being fixed and certainly is easily corrected. This should bring about a large quality increase however it may expose the limits of their optical stack (unknown!), Panasonic have had a long time making pancake lenses so they can't be that bad though.
I believe they are aiming for a fix this week or probably next week, that will then allow owners to actually give a full review then.
Pretty bad by shiftall how the software stack is so unfinished with poor stability, very much launched a few months too early or should have said it was a beta/development kit and that would have given them a lot more leeway in these particular problems.
So far it does seem the hardware is actually good albeit requires substantial dialing in, this is no meta quest where you just plonk it on and at most adjust ipd real quick.