No surprises here. Just like the lockdown on iPhone screen and part replacements, Macbooks suffer from the same Apple’s anti-repair and anti-consumer bullshit. Battery glued, ssd soldered in and can’t even swap parts with other official parts. 6000$ laptop and you don’t even own it.
So you’re drawing the conclusion that a more repairable device is inherently going to be worse than a less repairable device but that’s not true.
A sample size of two is hardly statistically relevant. Especially because you’re completely discounting the possibility that you were unusually lucky with your Mac or unusually unlucky with the Zenbook.
Gluing the battery in, in no way makes it last longer. The biggest problem here seems to be that the fan profile is not optimised, but that won’t have a significant effect on the battery because while it increases charge discharge cycles, it doesn’t increase them by that much. You probably just had a dud battery.