Is Mint Cinnamon supposed to be this slow to boot and install?

Cinnamon is heavier than Xfce, but that machine should be able to run it. Several minutes to get a usable live desktop and an installer that appears stuck for an hour are worth investigating, rather than assuming that's just how Mint works.

Since you've already tried two drives, check that the Mint image download matches its published checksum. Then recreate the installer. Etcher should work, but trying another image-writing tool can help rule out a bad write or a problem with the creation process.

I'd look at the boot messages first. In the boot menu, edit the boot options and remove quiet and splash, then boot with those changes. The messages may show where the long pause happens, which gives you something more useful to investigate than a black screen.

Note the last message before a long delay, though it isn't necessarily the cause by itself. You can share it along with how long the pause lasts.

Run a memory test and check the SSD's SMART health information. A tool such as GSmartControl can show the drive's reported status if it can access the drive. Those checks may reveal a hardware problem, but a clean result doesn't prove every component is fine.

The language package step could involve downloading updates, so a network delay is another possibility. If you can, try a wired connection during installation. That doesn't explain the slow live desktop on its own, though, so I'd still check the boot messages and installation media.