"it's far from dead I would suggest!"
I agree, but it is certainly a shadow of its former self and I reckon it's still deteriorating at a alarming rate, yes there are inroads being made but regards the roach, the populations are becoming so fragmented and apart from Cormorant predation, I've yet to hear of a fact based plausible explanation and one thing I am totally opposed to is the stocking of fish into an environment that they can't thrive in.
Regards the barbel and roach strongholds being different locations, yes and no. I've caught most roach from around Wimborne (low barbel numbers present) but I've also seen and caught plenty (in years gone by) at Longham, Muscliffe and Throop beat 1, all held reasonable barbel numbers. Throop beat 2 was always a bit hit and miss for roach and definitely offered some of the more prolific barbel sport.
This though goes back to my point alluded to earlier in this post; if barbel numbers are falling on say Throop beat 2 and it's a busy area, so keeping cormorants at bay, why are roach not filling that biomass void and at best, the chub are only just sustaining their numbers (certainly not increasing them).