Progress! I replaced the other 3 svgs (other than pcb) with the pi 3 versions and now pcb (without any changes) is properly scaled, it still isn't exporting correctly but for sure breadboard is also broken somehow and managing to break pcb which is weird. I'll continue poking (at the rp 4 for now, to make sure it exports correctly and I'm not copying something that doesn't work 
).
Peter