Hello Dess and thank you for your reply.
Indeed, if I do it programmatically, the text does change at runtime, which is great :)
"Segoe UI Light"
It could be a problem that only I experience (due to some other VS extension perhaps?), but at design time, if I try to do the same, i.e. on the form's Designer go to the RadTileElement properties, proceed on the "Font" property and click the "..." button for the font dialog to appear, no matter the changes I make, the RadTileElement's font won't change.
Now, knowing it's possible to actually change it made me think to not use the "..." font dialog and instead expand the font property and change the text size directly from there. It turns out this works too. So I can actually do it at design time as well.
Just please check out if there's a general problem preventing the font dialogue from passing the changes to the properties, because for me the dialogues are more intuitive and that's what I always tend to use
P.S. my problem is solved. Thank you :)