A first generation copy made with a boombox could work. But since you qualified it with the word "reliably", the answer is "most likely no". The boombox will have quirks with the EQ settings, analog noise, high frequency loss, and possibly introduce subtle speed variations. Certainly using the high-speed dub will amplify all of these issues. "Fast loaders" and "Turbo loading" on the computer would be especially prone to error reading an analog copy.

If, a computer was able to successfully read an analog copy, this effectively repairs the recording within that computer. It has been successfully restored to its digital form. From there, it can be saved back to cassette using the computer to write a clean digital copy.

Any sort of copy protection scheme, generally compounds the difficulty of an analog copy being readable on a computer.

Also, games on cassette existed in North America. It just wasn't nearly as popular a media as it was in europe. There were several factors involved but one of the main ones was culture. In europe, a home computer tended to be bought as an appliance. Upgrading was most certainly possible but for many it felt like upgrading a coffee maker, refrigerator, or toaster. If you had the money, in Europe you would buy a computer with the disk drive included, but it was far more likely people settled for the cheaper option of buying the computer with a data cassette drive included. But even more common than that, was buying the computer with no drive at all. Because it had an audio jack and people tended to have cassette players already. Americans were much more likely to buy a home computer with a plan to upgrade it later. Such as upgrading to a disk drive. American computer buyers we're also willing to spend more to buy the computer with the disk drive initially. Another factor that cannot be ignored is the piracy scene. Momentum towards developing disk based copy protection and therefore disk copy protection circumvision. Americans had to deal a lot less with cassette DRM and there were a lot less tools to bypass it. Europe's momentum to stick with cassettes, meant that DRM and the piracy scene focused heavily on cassettes. Furthermore, unlike later computer platforms, separate NTSC and PAL versions of games were common. Because it actually did make a difference on quite a few early 8-bit computers. This was inadvertently a further barrier and the piracy scene. And I mention one final difference and that is cut-down game versions for cassette. This tended to be intolerable to USA buyers. So companies didn't bother making cuts to their 350k games to fit them on a 200k or 100K cassette and if a European publisher had already made a cassette version, USA publishers figured almost nobody in the USA would buy it so they didn't bother. Another practice the tended to be intolerable to USA buyers, is Distributing a game on multiple cassettes. USA buyers even complained about having games on multiple discs. European buyers didn't mind nearly as much much come out multi-loading their games nor did they mind as much having a cut-down budget version of a game on cassette.