If you only get one engineer squad that's on you, take UKF sappers as a comparison, they are a flamer/piat squad, barbed wire, salvage, building emplacements, tearing down emplacements, building caches, snaring, blowing up cover, planting mines, defusing mines, repairing.
How is that any less than what the OKW pios do? Early game they turn engagements, they can put away their sweeper giving them back 1/4 fire power. What exactly do they do more of than any other engineer squad?
There are reasons why no good OKW player gets more than one SP. Whether it be bleeding to death at far range (30MP reinforce for 0.87 size CQC models), four man squad having to go close range & losing a greater proportion of its firepower per model drop, or being generally poor against people in garrisons/behind heavy cover. Then midgame arrives and 2 SPs will usually lose to 2 LMG equipped squads, esp if they have a BAR each. And so on.
They do most of what listed above and then a great deal more. Volks are frankly so abysmal that that a SP must fulfil the role of a mainline inf squad in every way. Flanking, stopping frontal assaults, dislodging dug in inf with grenade throws, zoning out CQC squads, taking early territory (GL with your volks and late MG otherwise), etc.
I liken the job of a SP squad to be a 'firefighter' where they are needed to put out fires in several places at the same time.
In any case, this stuff has been discussed to death by players far more experienced than myself.