Whenever I have travelled on the busway, albeit infrequently, it has always been the (slow) loading of passengers that has been the slowest part of the journey. The reduction of the speed limit from 50 to 30 has little overall effect on the time taken compared to the loading time at some stops.
Maybe it is now a greater proportion but there's no denying that the change in speed limits has impacted the journey time.
What Stagecoach have done is just use this as an excuse to cut the number of buses they run and therefore reduce the number of drivers they need to employ.
The problem, in my view, is that Stagecoach has really lost its mojo with the Busway, and dare I say it, with Stagecoach East as a whole, and apologies if I'm veering off topic on the safety element of the Busway.
I was in Peterborough bus station recently. The issues that I identified a few years ago are still there... The fleet is old - dominated by 10-12 plate e400s and there's not much newer. IIRC, there were some more 2017/8 e400mmc but they were moved to the X5. Peterborough's fleet is also much smaller and that's reflective of the wider business as they've incrementally ceded routes either in entirety or on a contracted out basis (like the 904). Appreciate that anyone can skew figures, and not wishing to talk about what the Romans have ever done for us, but aside from the 30 or so electric deckers for Cambridge, the investment into East has been woeful since Covid.
Moving onto the Busway specifically, it looks so jaded. The sites are looking tired and unloved, and so are the vehicles. The XLBs and Evoras are now just over 6 years old but you have 17 year old Eclipses still out all day. The image looks poor and there's little in terms of promotion or anything to tempt you to travel. It's just... there but slower.