Sure i agree with you, but the thing is Assault Engineer(which i assume you meant) and shocks are both doctrinal units and serve different roles in your unit roster, let's say you compare rangers and shocks which fill a similar role(if rangers go for Thompsons of course),shocks have nade and smoke nade and come deadly at close range by default, Rangers need to upgrade,have nade and can grab a bar(even with thompson), see not a great number of diffent abilities/utilities and if only counting active abilities the Rangers just lack a smoke nade.
Or if you go for a Axis/allies matchup you get Assault Grenadiers vs Shocks(closest matchup i can think in term of roles): Assault can upgrade to 6 man(veteran model) have Nades and sprint, while for shocks they have the nade and smoke nade. And Again i know the squads have different stats(armor,weapons and values) but they do serve similar roles.
Again nothing like the host of abilities/utilities the ISs can get compared to any other mainline unit by default.
There are plenty of situations where two units with similar purposes have different numbers of abilities.
LMG paras and LMG obers are similar- both are elite infatry with an emphasis on long range. What abilities do paras have? Well they have activated suppression, and they have cooked nades. What do obers have? They've got bundled nades, smoke nades, activated suppression with vet and booby traps. Oh and they are non doc.
Or how about non doc rifles vs volks? Rifles get rifle at nade and pinneaple, volks get faust incendiary nade and can build sandbags.
And interestingly sometimes when a unit has too many abilities it actually becomes problematic for that unit. Take sturmpioneers- they can repair, sweep for mines, build defenses, build landmines, offer healing for troops and have a stun grenade. I mean that sounds like a great unit right? No other engineer can give aoe healing, no other engineer has stun nades, no other engineer can get a minesweeper without sacrificing firepower. One could be forgiven for thinking that sturmpioneers are an OP unit. But they're not. There are other things that need to be considered before blanket declaring they are too strong.