TomTom and Magellan have angered a lot of people by dropping lifetime map subscriptions. At least Garmin has been better at that, I haven't heard any serious complaints from people with older automotive devices.
I think we are just seeing Garmin adapt to a rapidly changing market and allocate their resources to maximize profit. They probably think Basecamp is already "good enough", and I don't really disagree. But the problem with not being able to send maps to the GPS is outrageous. It just has to be a bug, and not something intentional. If they wanted to stop you from sending maps, they would just discontinue MapInstall, or have it put up a message that third party maps aren't supported.
So I'd guess it's just sloppy coding, because this problem never existed in old versions of the software. And by the time users started complaining, Garmin had already pulled the plug on Basecamp and assigned their programmers to another project. There is no incentive for them to fix this, aside from pleasing people who are using free third party maps instead of buying Garmin products. So they must be aware of the problem, but 7 months later, it hasn't been fixed and Garmin says Basecamp is finished. My interpretation is that Garmin just gave the finger to anyone who wants to use alternative, free maps on their devices.
Now you can downgrade to the old Basecamp, and that is the immediate fix for the problem. But that isn't so easy and the "average guy" won't know how. You can also use Mapsource, Garmin's older software. AFAIK, it still runs on current versions of Windows. This thread discusses the problem and how to downgrade:
https://forums.gpsfiledepot.com/index.php?topic=4539.0
I'm not clear on whether the same map installation problem exists with the Mac version, I have heard conflicting stories. But the current 32 bit Basecamp won't work on the next operating system the Apple releases in 2019. Of course, you don't have to upgrade to that new operating system, and probably shouldn't with an older computer anyway. But when Apple releases new Macs, they won't run older operating systems. So, for example, if Apple introduces a new iMac in November 2019, it will only be compatible with 64-bit apps and can't be downgraded to an older operating system.
There are still some work-arounds - for both Windows and Macs - such as running a virtual machine with an old operating system that is compatible with Basecamp. But that can also get complicated, and is more than what the average user will want to do.
So.... my take is that you will probably be able to continue using Basecamp with your existing GPS, although there may be additional hoops to jump through and bugs are not going to be fixed. At some point, Garmin may roll out a web portal that completely replaces basecamp for your older devices. But if you buy a new Garmin handheld, they are going to steer you towards the web portal and at some point, the new devices won't work at all with Basecamp. The link I posted above is specifically for the GPSMap66 handheld which was released a couple months ago. This is what they recommend:
"This web portal allows users multiple feature advantages. We recommend using the Explore Website for management of waypoints, locations, activities, tracks, and routes. "