Imho the internal SATA Ports are also slowly growing to become a weak point. Startup times on the 2012 mini have significantly increased with recent macOS incarnations (at least that’s my impression - never bothered to actually measure it) and Apple will increasingly design macOS for the 1.000, 2.000 or even 3.000 MB/s that modern SSD interfaces are capable of.
Over time, standard 2.5“ SATA SSD‘s will start to feel as „slow“ in comparison to NVMe drives, as HDD drives feel slow today in comparison to SATA SSD‘s. That weak point may even overtake the iGPU weak point, as people with only one monitor and/or 1080p display(s) will probably sooner feel the limitations of the SATA port than the iGPU limitations.
I agree. When APFS was still in beta, somebody posted an article here where they compared startup times to HFS+ and I was surprised how slow it was. Then when High Sierra was finally introduced, I don't think those times improved much. The last time I actually clocked my 2012 quad Mini booting from the original Apple internal 256gb SSD, I was still running Mountain Lion and it took 15 seconds.
The 2012 has a pretty slow internal SSD interface
2012 2.6ghz quad i7 Mini - original Apple 256gb internal SSD
The 2014 Mini is about 50% faster
2014 2.8ghz i5 Mini - original Apple 128gb internal SSD
Yeah, around this time last year I swapped out the 5400RPM hard drive in my Mac Mini because it was getting slow (especially with booting) with a 960 GB 2.5" SATA SSD that I was able to buy for just over $100. It really cut the startup time in half, and made opening applications a whole lot faster. This was when the Mac Mini still had MacOS 10.14 Mojave installed. So when I upgraded to Catalina, I had virtually no issues (at least once I upgraded my Tuxera NTFS software for use with external NTSF drives, and I found a 64-bit beta of the Boxer open-source DOS game emulator for the Mac OS.)