I don't think it's as bad as some are making out or as good as some others are making out.
In all the time I've been watching RL I've listened to people around me tearing into centres for not passing the ball when the centre has absolutely made the right decision. It's quite possible for a winger to have space in front of him yet still be covered by a defender on the inside (even if he is quick), but fans often don't recognise this. Now that this 'give it Grace' has become a 'thing', people are jumping on Percy to pass in situations where it really wouldn't be the right decision.
However, there have undoubtedly been at least two occasions in the last three games when Percy should have given Grace the ball but didn't. One of these was against Salford, and Percy immediately acknowledged it and apologised to Grace. The other was on Sunday, but not, for my money, the one where he was ankle tapped by Tierney. In that instance he looked as though he was about to measure up the pass - his mistake was thinking that he was clear of Tierney when he wasn't. The one that stuck out for me was in the first half: he made half break and had drawn the cover - if he'd have passed to Grace then I'm sure he would have scored.
For me it's not a big thing to worry about - I'm sure it will improve as both players are still young and learning to play alongside one another.