I, like many, have watched Melican through his career and hoped he would be the next Reg. Unlike you, I don't see it happening. Not because of repeat injuries and lengthy reacclimatizations but because of the lack of three really fundamental defensive attributes:It's reasonable to be optimistic that Paddy will show something, but that optimism should also apply to Melican finally getting an injury-free run at it. And if he is, then it's no competition between he and Paddy IMO, as I think the Tom x Melican partnership offers far more flexibility going forward than the Tom x Paddy partnership would (sorry to sound like the debbie downer ruining the McCartin brothers storyline!)
1) Anticipation of when and where the ball is likely to come in. This leads to him being caught out too often.
2) Slowish reactions. Combined with 1) he gets left on the lead far too often. But it also means he can't often peel off to make the third man with any confidence as Rampe often does.
3) Lack of composure. Too often, when caught out he uses physicality rather than technique to try to make up.for it and gives up a free.
You could put a different interpretation on his play, but that's how I see him coming up short of being a top notcher.