Self-powered drives larger than 2TB tend to be SMR types (high compression) and should not be used.
They are also a lot less reliable cf the big heavy powered drives as you call them.
I somehow dont like power ones. they are quite heavy
As intended to make them larger capacity and reliable and fast.
You cannot have your cake and eat it.
You cannot plug more than one self powered drive into a TC without a powered hub... in fact even one can cause power issues as the USB2 port is underpowered.
If you then try and plug multiple drives into it.. I can only wish you lots of luck.
Of course you could use multiple 2TB SSD drives.. as long as you have very deep pockets.
A proper NAS would be considerably cheaper.