Intels indium solder thermal conductivity is 80 w/mk. Intels polymer "paste" thermal interface material thermal conductivity is 3.5 w/mk, both specs available in intel whitepapers. Every PTIM cpu I have delided the temps drop by 20C which allows more overclocking headroom. Others results are same and expected given stim and ptim thermal spec difference. And the quality of intels polymer application, along with every other mass produced paste/polymer tim application is variable. Intel, per their own marketing person, came out in a youtube video which multiple forum posts have referenced, clearly stating cost was the reason for no longer using solder, not that it was ever a debatable point. Indium cost has increased and the use of stim requires an extra step/expense of metalizing the die surface for solder adhesion.That has nothing to do with the thermal interface material used. That's the CPUs not being of exactly equal quality, which has been some that most enthusiasts have exploited for OC'ing for as long as you've been able to OC.
Like, you've simply explained what anyone with access to many CPUs sees within one SKU... even soldered ones.
Granted, at stock, intels cpus dont require solder so overstating solder as necessary for anything but overclocking is a reach. But denying solders benefits of maintaining thermal headroom while overclocking is equally silly.