I think it's a little of that. We seem to want to strap on more protection but then lose mobility.Iirc the original aim of Warrior, Bradley & Co was to wait til the RA/AAC/RAF had blatted the baddies, before advancing in support of tanks, then debussing on the objective to clear and hold it, not to act as a glorified apc.
The early warrior training film showed this, using its weapons on strong points that bombardment and tanks had missed, while the tanks continued to advance beyond the ( infantry's) objective.
Perhaps doctrine or usage changed?
Would a modern, protected and manoeuvrable FV432 not be better with 8-10 blokes in the back? Capacity, protection, mobility.
If it needs firepower that could come from a supporting armoured car, carrying no troops. Protection, mobility, firepower.