I've always believed in KISS. I've said it before that Trainz has become way too geeky for many of us. This is supposed to be a train simulator and not a job and not something that requires a BA in Engineering and Computer Science to operate. I even made a recommendation that there be two operation modes. There could be a basic mode which allows for the simple stuff such as running routes and building routes without the extra baggage and then there is an advanced mode that is essentially what we have now.
For downloads, you can do a couple or a few at a time, if that helps much. I know that's annoying, and I feel the store interface is really in need of some development. How about a new items tab for instance? This would save time and make it a lot easier to find the new items available for download without scrolling through the gazillion or more that might be installed.
But why should you need to do a fresh installation? Your content is still there. What you need to do is use the browse option in the install tab by clicking on the 3-dots, to connect back to your database. Once that's completed TRS19 will want to restart and probably run a DBR, but you should be all set.
Layers are both a blessing and a curse. I hardly use them but there are many people who will use them for all kinds of things. Unfortunately, we can't get rid of them. For route editing, I do it the old-fashioned way and do the editing in the Route editor and rarely if ever use the new UDS unless I'm testing something. Other than that, it's switching modes to drive my session and edit in the route editor just like I've done since TRS2004.