This is definitely considering only the single-winner case. Proportional multi-winner elections are a whole different conversation.

Instant runoff, though, is directly considered here, so it's not an "other" solution, but rather an immediate part of this analysis. It doesn't perform very well in comparison to options like Condorcet, STAR, etc. As a theoretical comment, "ensure that the winner has a majority support" needs a very prominent qualifier: they only have majority support among the candidates that the runoff process doesn't eliminate first. Which, of course, makes the statements meaningless, since nearly every voting system chooses a candidate who has majority support among the candidates it didn't eliminate.