It's common for people to assume that if IBM didn't use a simple, open architecture with off-the-shelf components for the original PC, then we'd never have had the PC ecosystem as we know it.

But this view neglects the fact that an organic ecosystem of interoperable open hardware converging to de facto standards and running a common OS already existed prior to IBM designing their PC. By 1980, there were already many independent vendors implementing their own variation on the 8080/S-100 design pioneered by MITS, all running CP/M from Digital Research.

When IBM released the PC, the CP/M world was still going strong. The fact that it was an easily cloneable architecture based on the 16-bit 8086 caused a lot of disruption, and led to the market dynamics that were already present in the 8080-S100-CP/M world pivoting over to x86-ISA-DOS.

If IBM had kept their PC proprietary, it might have led to a bit more fragmentation in the short-term market for business microcomputing, but at the same time, the CP/M world would have continued on without that disruption, and something else would have ultimately catalyzed the move to a common 16-bit architecture. DR was already working on CP/M-86 at the time IBM was developing the PC, after all.

Eventually, the same forces that led to the collapse of vertically integrated, proprietary platforms and the dominance of open-standards system builders would have asserted themselves, and IBM itself would still have been subdued by them. Modern computing would likely be in a similar position with or without IBM. The PC was a major ripple, but didn't really change the current.