These threads appear every so often, sometimes without saying that you're meant to be going back in time to change things! There's always someone that thinks that CD-ROM drives were mass produced in 1992, and cheap!
Anyway, what I think is ...
The C64 was a major success, but what were they thinking with the Plus4? The Plus4 should have been a C64 with a faster CPU (2MHz for example), 128KB, 3.5" floppy and an enhanced VIC-II - maybe not to the level of the VIC-III that was never released, but I'm sure some extra colours wouldn't have gone amiss, nor an 80-column mode. This could have replaced the C64 in due course, whilst also being an affordable C64 upgrade for current owners during the years that the Amiga was quite a bit more expensive.
As regards the Amiga - the A1000 should have been promoted heavily. The A2000 should have had a faster 68000. The A500+ and A600 should have had faster 68000s. The A1200 should have come with fast RAM (1MB + 1MB). There should have been an A1400 with 28MHz 68020 and 4MB.
And they shouldn't have sacked all the engineers when they took over Amiga. Idiots.