This is not a big deal I think. Mikrotik is very stable and can run years but what advantage does it have?
I have learned it is bad to have such a long uptime. It means your router is not updated and running old software. So vulnarabilities are not solved.
Long uptime is to me... an impressive achievment in its own right!
1. This means stable power infrastructure and very good backup.
2. This means stable software, which is not easy to achieve. Even with the big Vendors, there are nasty and devastating bugs that just crash the system.
3. This means stablility and quality of the hardware, not only as a design, but also as production and quality assurance.
I do agree though, that it also depends on what the device does... if it is seating in a basement, just powered on, doing basically nothing - than it's not impressive. But if it's a real production device - that's an impressive feat.
Regarding the updates - it depends. Many vulnerabilities might just not concern your device, because it does not have the configuration or the configuration options that are required; you might not even have the packages that are affected in your system enabled. So... it depends