Transmission never broke. GNOME devs requested that Transmission break itself on non-GNOME platforms. Falling back on 'well you're not paying anything' really does nothing to dispel the perception that GNOME devs don't play nice with others. If anything, it cements it.
If nothing broke then I don't see what the problem is. And, your assertion doesn't even seem to be correct. I re-read the bug and it's one GNOME developer suggesting for changes to be made only in GNOME 3, because support for a particular feature was deprecated upstream. The developer is apologetic and later goes on to make suggestions about what can be done in Ubuntu and XFCE. I see nothing there about "GNOME devs requesting that Transmission break itself." https://trac.transmissionbt.com/ticket/3685
I'm not trying to dispel any perceptions either, if you have a deep seated belief that GNOME (or XFCE, or anything really) are "not playing nice" because they removed features from upstream, there's nothing I can really say to you to change that view. If you want to challenge your own perceptions, I'd suggest you start developing a new open source desktop and application platform yourself over a period of many years just to see how much work it is, and how it's practically impossible to support everything that every app developer asks for when none of them are paying you a cent.
If you're trying to illustrate the trend that GNOME and XFCE (and KDE, and LXQT, and MATE, and Budgie, and Mint...) all have different goals and ideas for how applications should behave then yes, I would say that much is obvious by now, and it has only gotten more obvious over the last few years. If you have a technical solution to this then I'd love to hear it, but aside from that I don't care to bicker about whose fault it is that your applications broke, because honestly no answer is going to pleasing for you to hear. Unless I'm mistaken then we aren't paying customers, this is all just random no-warranty open source and there's no support hotline that's going to care about what's broken.