Check https://parsoid-vs-core.wmflabs.org/diff/eswiki/Estaci%C3%B3n_Quilmes
https://es.wikipedia.org/w/index.php?title=Estaci%C3%B3n_Quilmes&action=edit§ion=6 is the gallery in question.
It looks like maybe there are different site defaults for media dimensions?
The legacy output has the same dimensions height="120" as Parsoid,
<li class="gallerybox" style="width: 152.66666666667px"><div style="width: 152.66666666667px"> <div class="thumb" style="width: 150.66666666667px;"><div style="margin:0px auto;"><a href="/wiki/Archivo:Quilmes_train_station_1890s.JPG" class="image"><img alt="" src="//upload.wikimedia.org/wikipedia/commons/thumb/a/a6/Quilmes_train_station_1890s.JPG/226px-Quilmes_train_station_1890s.JPG" decoding="async" width="151" height="120" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/a/a6/Quilmes_train_station_1890s.JPG/339px-Quilmes_train_station_1890s.JPG 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/a/a6/Quilmes_train_station_1890s.JPG/453px-Quilmes_train_station_1890s.JPG 2x" data-file-width="1728" data-file-height="1375" /></a></div></div> <div class="gallerytext"> <p>La estación original, en la década de 1890. </p> </div> </div></li>
but there's client side scaling.
Looks like it's happening in https://es.wikipedia.org/w/load.php?lang=es&modules=mediawiki.page.gallery&only=scripts&raw=1&skin=vector&debug=true
But scaling also occurs on enwiki ( see the gallery on https://en.wikipedia.org/wiki/Amazon_(company) ) so I don't think it's anything to do with a missing site config. It's just part of the module mediawiki.page.gallery
Interesting ... I suppose the bug then is why the mediawiki.page.gallery is not applying to Parsoid galleries in the visual diff code ... but, I'll take a look and see if there is a bug in how I'm enabling the modules.
I suppose the bug then is why the mediawiki.page.gallery is not applying to Parsoid galleries in the visual diff code ...
That part is filed as T272186 (see the fourth bullet)