> catastrophic loss of downforce if they got too near other cars. The drivers had to work around this by not following too closely

While the downforce loss was significant, it was predictable and could be easily avoided. The equivalent for ground effect, e.g. hitting a bump or curb mid-corner and lifting the skirt just far enough for the pressure seal to fail and your downforce to go from 100% to near 0% in an instant, is far more likely to lead to a catastrophic accident.