The motor is never in a strain.
As I tried to explain before (maybe not clearly) the motor is under it greatest strain when nothing obstructs the flow of air. This is no different then any pump that pumps liquids, air, water, oil etc. If you start to limit the air the motor will unload and speed up. All the regulator is doing is allowing the air to come to the motor from another source so less comes though the vacuum hose but the same amount goes through the motor.
My objection to the peg board is that it is an obstruction and I can see no reason for it. Take it out and you can use a much smaller motor. This will allow you to use a longer extension cord which I think would be an advantage.
I understand what you are saying and what you say is reasonable in the type uses you are describing with construction equipment etc. I feel I have failed to help you understand the function of the pegboard in my home build (colorado type) bee vac situation. I will try to explain on the terms you understand and are familiar with. I have noticed on my air compressor, (the 6 gallon pancake one), When no air pressure is in the tank and first turned on it is allowed to run at a faster, full, rpm because there is no load build up at first speaking of psi. The motor is allowed to run the full rpms it was designed to run at. As the psi slowly builds up, then the motor begins to slowly slow down in rpms the more load, the more psi realized, the slower the rpms and motor load until finally, the motor shuts off at 150 psi. By this time the motor really sounds to be under tremendous strain. With the bee vac and peg board in comparison, this type of load is never an issue or achieved with my homemade bee vac. Compare the two, reset compressor max setting to 10 psi instead of 150 psi of compressed air, then the compressor motor immediately shuts off at that 10 psi new setting. No strain is ever realized. This comparison reset should give us a fair comparison to the pegboard function of my bee vac because only a fraction of the output of the beevac is required. Remember, we only need enough suction to get the bees through the hose and in the catch box, without injury to the bees, along with the happy medium of arriving in the catch box without getting stopped up in the hose.
We can use a car for another example or any or any other type motor as you have stated. Let us look at a car engine for instance, going up a mountain as compared to a small grade. Start up a mountain and the higher you drive the more energy it takes to get up that mountain and the more the "strain" is realized by the driver. Now go up a small incline of only a few feet in height and there is a strain, but a strain that is almost not noticed. Compare this analogy to the extra energy of pegboard and bee vac and it is like comparing the difference in the strain of the mountain, and slight incline of the vehicle example. You will not hear a difference in motor strain from the car and you will not hear the difference of vac motor strain with my vac. The pegboard does allow plenty of air flow to the catch box area, there are hundreds of peg holes in this board. The only yet simple function of the pegboard is to adjust if you will, or regulate the already low needed suction pressure to be sure to get the bees safely and efficiently through the bee vac pool hose. Any needed suction is only enough to get the bees to the catch box through this hose, gently and safely. Any unneeded vacuum of the motor is released through the suction relief valve, assisting in no added, unnecessary strain or suction of the be vac apparatus, diverting any strong vacuum we do not need or want in excess of getting bees in the bee vac catch box, affording no damage to the bees.
The only simple yet unique purpose of the peg board is to assure an even, suction of pressure, throughout every square inch of the 16" wide by 19 7/8" long 9' tall catch box. The peg board can be viewed as a regulator if you will. No matter where the bee is in the open catch box, it has little to no strain from the vac itself because every inch of the inside of the catch box is at an even regulated suction pull. In theory, there is no one part of the catch box that has more suction pull than the other. This is why no foam is needed on the opposite end of the catch box. The bees do not come crashing in the catchbox. The instant the bee enters the open even pressured catch box, it is received with a soft gentle landing because of the regulated air of the pegboard. Unique really. Bees do not have to deal with being pulled here and there, too or fro inside the catch box. Because of the added help of the even suction of the "regulated" peg board air. If I need to go back to the other topic and copy and paste here to assist in my explanation I will be happy too.
I hope that helps you understand the function of the pegboard. (at least on my homebuilt vac design)