@Stocky For what its worth, mammut, scarpa, la sportiva, etc all buy the exact same gtx liners from the same company—the waterproof part of these boots is literally the same part purchased from WL gore, off the same production and even from the same production batches. There may be construction differences in assembly that cause one boot to wear differently than another company’s or model of boot from internal abrasion, which can also be related to fit differences from person to person, but the tech and the part itself is literally the same. If you experience one boot like that losing waterproofing well before another, its either a faulty construction (a cut or puncture in the liner not caught in qc, a weird fold that caused premature wear inside the boot, etc) or its a peculiarity of the way the boot fits you that is causing an abnormal flex-point inside the boot that is wearing out the waterproof liner.
I’ve had a dozen or more pairs of mammut mountaineering and other types of boots (I used to work for Mammut), the fit tends to be pretty spot-on with a couple foot-shape caveats: 1) if you have a particularly longer big toe or second toe compared to the rest of your toes, you may need to go up half a size to get the length you need. This is me. 2) the mammut lasts for technical boots in particular are a little more curved than some others—so if you are wearing your boots looking down on them from above, the last curves in from the outside edge of the foot, toward the big toe, more than others. If you have a foot shape that isnt well suited to this last, this will manifest as feeling like it is too tight on the outside side of your foot behind your little toe, or feeling like it is a sloppy/loose fit on the inside of your foot and big toe, or both of those things. Some people end up going to a larger size because of this, but its much more of a last-shape vs foot shape issue, than it is a size issue, and adjusting size as a result of this may cause other problems (see above comment about weird folds or flex points in boot causing premature wear, etc).
Comment above about rubber hardness and resulting grip on rock (wet especially, but also dry rock) is spot-on as well.