GPS (excluding waas laas dgps) is primary means of navigation, my statement was on GPS only
In that case, then yes, you are correct.
However, lets look at the enroute case.
L1011 aircraft equipped with dual Honeywell HT-9100 or Universal UNS-1M GPS navigators.
Fully approved for MNPS north Atlantic ops as a sole means of enroute navigation...and this was over ten years ago.
I suspect that other aircraft/equipment combinations were as well.
Dual Omega equipped aircraft, is another example.
Now, having said this, usually these aircraft were also equipped with INS units, but not always...and not specifically required by the ops specs issued to the specific carrier.
Now, a few will say...never.
Oddly enough, there usually are exceptions, fully approved by the relevant regulatory authorities.