Jon Hopkins headlined the second stage at Latitude a few years back and was very good. I’ve no doubt he would still be excellent, although objectively on paper he is a weak main stage headliner.
On the subject of Latitude, in 2019 they had Underworld close the main stage and billed top but the actual headliner was Stereophonics before them. This year Keane were presented as headliner but are actually subbing for London Grammar. I appreciate GM and Latitude are not the same, but it shows the standard billing model isn’t the only way.