On the wiki we use multiple levels of headlines (= title1 =) to structure our content. Sometimes for styling reasons we don't use the exact next headline level. I.e. from (= title1 =) me might not go for (== title2 ==) but for (=== title2 ===). The hierarchy stays intact and it's 100% clear for the reader which headline belongs the which parent headline.

However Google Pagespeed and lighthouse reports:

Heading elements are not in a sequentially-descending order

Can MediaWiki fix this problem on the wiki level?

As MediaWiki is currently implemented, = title1 = becomes h1 and if followed by === title2 === that becomes h3. Therefore h2 is missing from Pagespeed / lighthouse. Could MediaWiki use h2 if === title2 === in case there is no == title ==?