What I'm seeing is that as third-party shipping SW gets better vendors are able to use multiple shippers to optimize for each shipment.

AFAIK it used to be that the main source of shipping SW was the courier companies themselves, which pretty much guaranteed lock-in.

M60ti, VP180, QS8, M2ti, EP500, PC-Plus 20-39
M5HP, M40ti, Sierra-1
LFR1100 active, ADA1500-4 and -8