I wonder when I experience noticeably degraded model quality, ie opus, is it because my usage falls in the highest buckets and I’m being shadow limited or served worse versions of opus or is it because of actual server load/burden?

It wouldn’t be the first time companies have secret shadow algorithms running to optimize things and wouldn’t it be obvious to limit power users as matter of cost/profit and not tell them. (See history of “Shadow ban” though that’s for different reasons)