I think the correct answer is “It depends”.
All ports have a speed limit. That includes the port you plug the hub in.
If the sum of the throughput of your drive exceeds that of the USB connector in your PC then speed will be throttled.
Keep in mind there are several USB3 standards with a great variation in max. speed.
If you would access all 4 drives at top speed the limit may be reached, depending on the speed of the drives which I don’t know.
The other potential bottleneck is the hub itself.
Is it’s electronics fast enough to handle all that data.
So there are a lot of factors in play here.
But none of all of that may be the real speed factor.
I’m fairly sure (not 100%) that the plug that goes in your PC can only handle one data stream at the time. Can anyone verify that?
So say you are doing some copying between the 4 drives and they are all busy at the same time, then your PC will only receive data from one drive at a time. To you it looks like all drives are working simultaneously because they are rotated quickly.
That in theory has a negative effect of speed. But only if the drives come near the max. speed of the hub and port on your PC. Buffering inside the hub may improve that but I don’t expect that to be present.
But otoh, your drives likely aren’t all active at the same time.
Anyway for drives it’s always best not to connect them to a hub but directly to your PC. Then use a hub for slow stuf like your mice, scanner, printer, usb sticks, etc.
Use a USB2 port for that and keep your USB 3 ports for the drives.
I really would like to suggest to consider that last paragraph very well. After all ever step, always slows down. If not speed, then latency.