Yes, the best case scenario might be an extremely mild disease that gives everyone natural immunity to more virulent strains. But half as deadly with twice transmission rate is kind of a wash, in the short term right?

But if R > 1, eventually everyone gets it and has their lottery ticket drawn, so increased transmissibility just speeds that process up (unflattens the curve). With the vaccines, R was < 1, so it would have petered out. That scenario looks out the window.

I think its a little early to be making confident predictions. Lots of potential confounds, e.g. while hospitalization rates have been lower in South Africa, I believe that the demographics have skewed younger than in previous waves too.