They actually have a whole bunch of repair abilities. On top of cheaper engineers to start with, there's also vehicle self-repair, conscript repair, and windustry's repair stations.
I said only about industry since conscripts are generally not worth it in numbers right now so conscript repair is not that much used and vehicle self repair is problematic to use becouse you can't stop it and it doesnt repair if infantry is shooting at the tank, meaning its much better to just buy more engies even if you have the doctrine. Non-doc T-70 self repair is different and much better but we are talking about repairing heavies in late game.
Also, this are all doctrinal abilities, and main soviet IS-2 doctrine (shock rifle frontline) doesnt have any of them, while in case of ostheer all tiger doctrines would benefit from nondoc repair buff. As for engi cost - pios are both better at fithing and can scout, there is no reason why they should cost the same.