I remember watching that GCN vid back when it came out.
My off the cuff tests years ago consistently had me climbing about one gear higher with clipless vs flats, more or less one gear, and pedalling more "in circles" seemed to make my various leg muscles feel better.
It would be interesting to do the same climbing tests again now 25 years later, but like I said, foot retention and hammering in a sprint for a light with foot pullup combining with pushing down is something I enjoy, and the foot retention thing is a big plus for me also, as I barrel over all kinds of stuff on my commute.
Heck, a few winters ago when I made the decision to keep riding in the snow, as prep and continuing riding to keep the legs in good shape before a late jan. departure for a long touring trip, I actually started with removing my spd's from my mtb, but after one ride, it just felt weird and went back to the clipless.

yes, there are times riding snow or really technical stuff that not clipped in can be nice, but for all the rest, I still prefer clipped.

and to go back to my views on clipless when climbing, I have done a lot of loaded riding in mountains, and I find the changeup of pedalling style that clipless allows makes a real difference to my leg muscles comfort over hours and hours, and I feel it helps maintain a higher cadence, which has a knockoff benefit for knees and knee muscles (Ive got a dodgey knee a bit, and so again, appreciate every little bit-even if it is whatever percent of an advantage)