I liked Rouvy too–the real world video part was pretty attractive. Didn’t ride it enough to get a feel for drafting or anything, but it was cool riding through actual Spain 
I get your point about the gamification. I just never saw it as immature to be motivated by these things. I train a lot, and historically I’ve been able to force myself to train indoors when the weather isn’t conducive to outdoor training (I’m in the US midwest–winter riding is one thing, winter training is another). But I also do find those elements you mentioned motivating to varying degrees, and I don’t see that as problematic. I’ve already used PRs on various roads or segments IRL as motivation, so seeing if I can do better on a segment seems natural to me. And I also use other riders IRL as motivation. Not in a ‘competitive jerk’ way
But if I’m going hard, and someone passes me going significantly faster, I’ll try to see how long I can keep them in sight. Using people as ‘rabbits’ IRL has also just always been a thing for me.
As far as the items and such to unlock–yeah, it’s contrived, but it’s not like it’s a secret or hidden or sneaky attempt to motivate. Some people are motivated by achieving goals, regardless of the goals. In fact, I’d argue that most people are motivated in that way. Just look at how ‘getting likes’ on an Instagram post motivates people, right? I know cyclists who count the number of centuries they’ve ridden, or the number of tires they go through in a season, or the number of meters they climb, simply because people tend to be motivated by checking items off lists. (I tell my students that all the time when they have motivational problems with getting their work done–make simple lists of the stuff you have to do each day, and check it off as you do it. It’s motivating for most people.)
I don’t say any of that to say that you have to like or appreciate any of it, of course
I just don’t see any of it as particularly immature, so it was ‘sophomoric’ that made me curious. If someone gets motivated by unlocking new kit, and that helps them keep a regular schedule of training, I don’t see why it’s not a thing for normal adults to do. For me, I’ll say this–in the past, using TrainerRoad for example, I would force myself to workout. I’d tell myself “I have to train, get up there in the pain cave”, and I’d grit my teeth through an hour. Since starting Zwift, I find myself saying “Okay, I have 45 minutes”, and then 90 minutes later I’m saying “I really need to stop now, I’m going to be dead tomorrow”. And my FTP is 20 watts higher than it’s ever been as well. So it’s not only getting me benefits, but it’s faaaaaar more enjoyable–for me, not for everyone–than other indoor training I’ve done before.
All of that said, I get where you’re coming from. If you don’t like those elements, then the screen putting them up in your face would be annoying. It would be cool if Zwift’s UI was super customizable, but I think they have bigger fish to fry than that. Or, they just have their own preferences about what it should look like.