"Jack
Well, it might need some supporting tweaks as well, but I think that's the main issue (the disadvantage of the extra fuel on the hard tyres).
Another reason I think everyone is probably using the softs and super softs at the moment is the weather system. As winter has arrived in the northern hemisphere, we've got a chill over most tracks. Developing our own in-house weather system might also be beneficial to strategy variety. The Hard tyres were never meant to be fastest in cold conditions, and the soft tyres were never meant to be fastest in hot climates and high wear tracks.
Funnily enough, the hard tyres had too much of an advantage in testing, which was why they were originally slower right after the update. We put all four compounds (at their current performance levels) on a grid of 4 teams, split each running one of the compounds. The teams were identical in every way, down to all the individual stats of the drivers. Then we ran dozens of races where the hard tyres came out on top above a certain temperature (I remember using Australia, Malaysia and Italy in the test). It just goes to show, you can never fully prepare for what goes on in a live environment. The moment we put it live everyone has said how poor the hard tyres are!
And even over a year later Hard tyres are still going poor lol.
Thankfully New iGP has seen big improvements and lot's of tweaks to the tyres!