They were still good windowses for their time, especially when you compare them to DOS and Mac OS 9 which would have been the alternatives.
For a fair comparison with professional OSes with full memory protection like UNIX you’d have to look at Windows NT, but there the preimise is true as well (as far as I can tell by googling, I only ever used 2000 Pro): 3.1 was bad, 3.5(1) good, 4.0 bad, 2000 good, 2003 meh.
Prior XP they were really bad at memory management and isolation.
They were still good windowses for their time, especially when you compare them to DOS and Mac OS 9 which would have been the alternatives. For a fair comparison with professional OSes with full memory protection like UNIX you’d have to look at Windows NT, but there the preimise is true as well (as far as I can tell by googling, I only ever used 2000 Pro): 3.1 was bad, 3.5(1) good, 4.0 bad, 2000 good, 2003 meh.
There was also OS/2. But yes, for the time they were running decently on “cheap” hardware.