You said two players playing the same amount, the longer they loot each day the more it favors the TH9. Regardless of how much loot the TH10 is getting in raids, it would be more at TH9 due to no loot penalty... for example the 600K base you hit would have been worth 660K if you were TH9.
You make a good point about the loot penalty, not to mention the TH10 has to spend more per search for their raids than TH9. But....
Stronger troops are irrelevant for looting purposes... I rarely used half my army per raid and could normally go non-stop. Finish one raid, start searching for the next one.
Ain't nobody got time for that! Unless you have the luxury time to BARCH 24/7, I actually use a more flexible army at TH10 when I raid, because I just don't have the free time to raid nonstop. So my army has giants and wizards, wb's and goblins in the mix as well as archers and barbs. It gives me the flexibility to hit someone for collectors that are exposed and full without using the full army, or having a flexible enough army that I can breach cores and raid protected storages.
The TH10 is going to have a much stronger army to accomplish that sort of thing, and is likely going to be hitting targets with more DE than the TH9 will be (since the TH9 will hit more TH8's than the TH10 will hit them).
Now, if you're talking TH9 vs TH10 both barching non-stop, the TH9 comes out ahead, I can't argue with you there.
The only thing that changes is the order in which it's done... the TH10 will be pumping those same walls while the max TH9 (now TH10) is doing those same 7-14 day upgrades.
If player 10 stops at skulls while player 9 goes on to lava that means P9 has idle builders and starts upgrading an additional 1 billion loot worth of walls while P10 starts on their TH10 builds. Once P10 has his new based maxed he will now have the idle builders and 1B worth of walls to pump out... and he is facing that 1B required loot with a loot penalty. P9 is doing his TH10 builds while P10 is pumping the walls P9 has already done. P9 will reach maxed TH10 with lavas before P10. Builders twiddling their thumbs at TH9 or at TH10 are still twiddling their thumbs. One has finished working while the other one is taking a break but they both end up taking the same amount of time off.
Again you make a solid argument. I would counter that the TH10 has extra drills/collectors that pump out the following per day more than the TH9:
Gold & Elixir: 84,000 more per day
Dark Elixir: 2,400 more per day
In addition, a TH9 waiting to max EVERYTHING is likely going to be spending the biggest chunk of their time on maxing walls and heroes. It's possible they will cap out their research, leaving the lab sitting idle. And the TH10 is going to be more likely to be raiding a significant amount more dark elixir than the TH9, given that TH9 is going to hit a lot more TH8's in their raids.
But, as discussed, everyone has their own approach to achieving fun in this game, and that should be what matters to each.