This doesn't change the fact that, for any degree of heat conductivity achieved smaller packages will be hard to keep cold than large ones.

It also doesn't change the fact that smaller devices are harder to put wires on - but they're both polynomial scaling factors that other polynomial scaling paradigms could cancel out.

The topic of discussion is datacenter vs. an extremely small cryocooler. What is the other polynomial scaling paradigm that would cancel out the datacenter's advantage?

The effectiveness of thermal insulators and heat pumps. If they make the cost difference negligible then other costs will dominate. We're talking about future decades of material science advancements here, a lot is possible.