Diffs like https://en.m.wikipedia.org/wiki/Special:MobileDiff/665979469 shows a lot of messy wikitext, e.g.:
> Reverting possible vandalism by [[Special:Contributions/..|..]] to version by ... False positive? [[User:ClueBot NG/FalsePositives|Report it]]. Thanks, [[User:ClueBot NG|ClueBot NG]]. (2266825) (Bot)
Note that edit summaries have a narrow restricted subset of allowed syntaxes. And desktop diffs do render them.
The mobile page history page also doesn't render the links, but at least it doesn't display syntax either. The mobile history page seems to use the parsed html and then strips html for plain text:
That would be preferable to unexpectedly exposing wikitext, though ideally it would just be rendered. As far as I know the API already exposes this alongside the raw edit summary.
Note that there is one place where Mobile-Web does render the edit summary. Namely, the oldid pages: