Bagan played left back/left wing back for Cardiff whenever he was fit
https://www.transfermarkt.co.uk/joel-bagan/leistungsdatendetails/spieler/742163/wettbewerb/GB2/saison/2021
Giles filled in at LWB when Bagan was injured, but Giles is much more a winger than a wing back/full back, which is only emphasised by how badly Cardiff's defence performed during that period,
Although as you state, most of his assists for Cardiff were from set pieces, so maybe he was nothing more than a set piece specialist who doesn't offer much from open play... quite why he couldn't provide a few assists from set pieces for Rovers is a mystery though eh?