That unusual, though tbf I think 33/34 is slightly long inside leg than most, as I’m 6ft odd with a 32″. I am surprised you couldn’t get the seat posts up high enough on the G-160 though, I own a ‘medium’ Whyte HT which is fine for me, so wouldn’t expect issues on a Large. This could be quickly resolved with a longer seat post or longer travel dropper post (depending on what was fitted). I do know that Whyte have gone really long on the eTT’s this year, so may not be the best to compare the cube with though..
With your longer inside leg, that bit more post will increase how far away you are from the front of the bike, so maybe a cube would work for you. TBH I think it takes a bit of time to get used to a changes in geo, like a longer eTT, so a short(ish) demo doesn’t really sell it that well. I moved up in sizing (L to XL, that medium was weird sizing), as I looked at my previous bikes eTT, my stem length and the seat being so far back on the rails, I wasn’t in the efficient position over the BB.
You back situation may well be elevated by a short TT, only you can tell if you comfortable and that more important than an efficient position.