The animations are clearly showing now with visual clues that you are going in the app, a layer up, a layer down and back out again.
Your post would make more sense if the concepts of "layer up" and "layer down" were concepts WP actually supported in the way you are thinking about them. Although that might adequately describe iOS' concepts of popping in and out of apps, it's not a valid description of WP. The reason you think those animations are
clearly showing you anything, is likely because you associate
clarity with familiarity, or at least more so than you associate
clarity with either correctness or expressiveness (in this particular case, I take expressiveness to mean the degree to which WP's UI visually communicates the existence of and concepts underlying the back stack).
If sacrificing UI expressiveness is what it takes to make W10M's UI more accessible to iOS and Android owners, so be it, but I doubt this will make any difference whatsoever. IMHO MS could evolve WP into an iOS clone, shedding every last UI unfamiliarity you can think of, and that still would not move the needle. Why? Because the main problem has never been that WP is too inaccessible for iOS or Android owners to
use, but that many of them see no reason to.
AFAIK, the back stack on W10M is no different from the back stack on WP, i.e. after navigating forward, away from the current page, it's often not immediately obvious where pressing the back button will take you. To a previous page in the current app? Back to the previous app? Back to the start screen? This is the kind of thing animations would be great at conveying, but instead of making that clearer, W10M is doing the opposite. It was never perfect, and recently a lot more inconsistencies have been creeping in, but now the animations no longer even attempt to convey any of that. The animations now have less meaning. They have lost most of their expressiveness.
You apparently view this as a good thing, but I think you are mistaken. You had/have problems understanding the back stack on WP. I suspect the new animations suggest to you that what you're unfamiliar with is going away. IMHO that's the worst possible approach. It would only be the right approach if the unfamiliarities actually were going away, but they aren't (W10M still uses the back stack). IMHO MS should be doing the exact opposite. The fact that
UI navigation is different and you had trouble grasping those differences, means MS must do a better job of explaining them, precisely by providing more visual queues showing how navigation works on WP, possibly sometimes being very direct about it, and enforcing their consistent application throughout. This would allow MS to stake out some rules, which MS could make explicit, stating how navigation on WP works (you see animation A, the you can know the back button will take you to where you previously were). MS could also demonstrate these rules in an interactive tutorial that runs after initial setup. MS could also ensure that demonstration was installed on all devices on display in stores, simultaneously showing off its benefits.
Anyway, I hope I could convince you somewhat. Just to be clear, I'm not saying you're dense or to blame for any of the acclimatization issues you had on WP. I'm saying WP wasn't good at getting you past that phase and IMHO W10M is not going to get any better at it...