You're defining "useful lifespan" of the Apple very differently than the Xbox. You're defining the Apple by how long development tools are supported, and while that is a valid criticism, it is the same duration today as it was when you bought the laptop. By the metric you're judging the Xbox, the MacBook Pro can connect to the internet, can run programs, and can connect to Apple's consumer services the same as it ever could. Its life as a consumer device is far from over. I'm typing this on my pre-retina 2012 MacBook Pro (running Linux).

You've said the machines "sole purpose" was development, yet you chose upgrades not essential to that process; the absolute fastest chip at the time and a larger SSD are arguably not necessary for the machine's "sole purpose." And the expected lifespan of the machine by that metric is no different today than when you bought it. Hate to put too fine a point on it, but you choose to overspend on a tool and are upset that the tool didn't ROI your inflated expectation.

Apple's decision to require a Mac for development and "only" supporting for seven years is absolutely worthy of critique. But it's also been consistent, and I'm sorry you didn't factor that in when you bought the machine. Sounds like you're done developing for iOS; I don't blame you. But if you decided otherwise, you can get into a development machine for probably not too much more than what you can sell your 2019 MacBook Pro for. Mac mini (if you can find one) and even the Neo will run absolutely hog wild over the performance of your MBP.