I said on package memory(not enough alone but LNL has PHY optimizations) alone is enough for 0.5-1W reduction which is substantial.
20-30% reduction makes it closer to Meteorlake than Lunarlake, and that's a huge amount. You are going from 15 hours to 10-12 hours.
What I mean by "20-30% especially in specific light-work loads", is that a 20-30% difference is mostly going to be seen only in very specific scenarios in which the workload is extremely light and constant for the 12hr+ test. In actual use where you have a mix of workloads, PTL will likely continue to keep up with LNL much better than MTL could. Either way, battery life is a separate discussion from power-efficiency. Zen 4/5 has been much more power efficient than ADL/RPL but if you look at idle power consumption and certain light workloads like media consumption tests, ADL/RPL is superior meaning battery life on those CPUs would be better.
Regardless, if your definition of power efficiency is only dictated by 12HR straight of light web-browsing or streaming 1080p video then our disagreement is just about semantics. When I talk about efficiency i'm not just talking about battery life in ideal scenarios I'm talking about power/perf curve behaviors, of which PTL will be incredibly similar to lunar-lake since they possess similar core architectures and core layouts and 1-2W of extra power from lack of MoP, PMICs, and possibly inter-core power loss is going to be negligible in a lot of circumstances. Limit Panther/Lunar/Meteor to 17-30W and run any workload and you'll see that PTL and LNL are off in their own world with MTL far behind.
I told you the inter-die communication effects aren't necessarily about pJ/bit differences but the increased latency which prevents the CPU from entering/exiting states as often. Nothing is instant, and you are increasing that part, meaning more time in high power active and less time in low power idle, and for modern processors it works even in moderate usage scenarios.
If you are talking about increased latency in regards to having LPE off the compute tile, like I mentioned it's not a given that the LPE cores are actually off the compute tile same as it was on lunar-lake, and even if they were, they might be able to do what Intel originally intended them to do on meteor-lake, which is to be power enough to actually take over during light-workloads and completely turn off the compute tile. In that case, panther-lake might actually have a battery advantage over Lunar-lake regardless of increased latency, but I doubt that's what they are trying to do this time around.
Skymont can be very power efficient, but it has to be in a same format as Lunarlake did. The regular E cores are just like predecessors and meant for extra performance, and zero about battery life, meaning it's up to the LPE cores.
PTL-U has 4 LPE cores same as Lunar lake does, and it's possibly on the compute tile too, so IDK what you mean.
By focusing on finances again Intel is potentially losing much more by not stemming the increasing ARM on PC threat.
I hope you aren't thinking of Snapdragon or M-series chips as a threat to the x86 PC market. The only possible contender might be Nvidia, but that's up in the air since we literally know nothing about their plans.
Dell on the leaked roadmap shows that they themselves also agree it's NOT the same as Lunarlake and will be significant regressions in that regard.
If you are referring to the leaked roadmap in May, I really don't see how you can extrapolate that PTL-U will not be competitive in power efficiency compared to LNL. In the first place it doesn't seem to be entirely accurate since it shows LNL XPS 13 being introduced in 2026 Q1 at the same time as the XPS-14 with PTL which makes no sense since the XPS13 already has lunar lake in it. Also they have meteor-lake being used in lieu of ARL-H and PTL-H which makes zero sense if you watched a single review of MTL. So yea, I really wouldn't put any weight into anything on that roadmap.
Besides, Lunar-lake likely is still superior to PTL-U when it comes to battery life and graphics, while offering competitive perf/power to PTL-U. So I would not be surprised if they kept using lunar-lake in their premium thin & lights post panther lake. Although personally as a consumer, I would much rather purchase a panther lake laptop with slightly less battery life