Heck I never heard of a 100% group 5 oil. I always though of a group 5 petroleum product as an additive to engine oils (like ester). Of course you have this crazy marketing with Amsoil that says they are classified as a true group 5 oil. I actually have no clue as to what is truthful.
All I know is my anecdotal experience using high quality ester based Motul 800 2T and 300V in hard core trail conditions where temps on the bikes reach high temps and in one case lost all my water and was able to make it back to my truck with no engine damage.
I don't recall AMSOIL ever claiming they were blending lubes that were predominantly Group V, they used to mention PAO (Group IV) but stopped doing that. Their Signature Series is typically understood to be PAO-based, while the lower priced oils are Group III based.
Group I is typically a solvent dewaxed conventional base with a low VI
Group II is solvent dewaxed or hydrocracked conventional bases with "medium" VI's
Group III is anything hydrocracked with a high VI, including GTL
Group IV is just PAO, that's the only base in that category
Group V is anything that doesn't fit in the other groups, so this includes AN's, POE...etc. Most people think of POE when they think of Group V.
No PCMO or HDEO is going to be majority POE because it has a tendency to swell seals, which is definitely not desirable. It works the opposite of PAO, which tends to shrink and harden seals. That's why PAO typically will have POE added to it in sufficient volumes to counteract that effect and balance it out.
Seal swelling isn't an issue in jet turbines, where POE-based oils are used.
A few brands advertise that they use Esters in their base oil blend, but none of them mention how much. A lot of folks thought that Redline was majority POE, but the MSDS sheets suggest that it's majority PAO (which makes perfect sense). I suspect the game is similar with Motul, except they use Group III and PAO with some POE added to it and then call it "EsterCore". This prevents it from being called "Full Synthetic" in Germany.
Mobil's old Tri-Syn formula was exactly that: three synthetic bases, PAO, POE and AN's. Later formulas incorporated Group III and more recently, GTL. They would still use those other bases, in whatever quantity yields the desired result in their performance testing, as they produce all of these bases (except GTL) in house.