unlike Hayne, due to his age Holmes has a chance to actually make it over there
He's going to have to commit to it and be ready to put in 2-3 years of work for little to no return in hopes of being a player by 25-26.
As i said with Hayne, the probably is never really athleticism with guys like Holmes or Hayne, they're athletically capable of being good players (though our freaks dont stand up athletically to theirs for a number of reasons, including the level of facilities and coaching their athletes get at a young age compared to ours)
The problem is these guys dont know the game, they dont play it naturally, they have to think about what they're doing, and whilst ever that happens, they're a second too slow and in a game that is made for bursts of 4-5 seconds of action, 1 second too slow is too much.
Holmes will need to get onto a roster, get the practise reps and be willing to keep working on the reps until he's natural in what he's doing, where he can just go out and play as he sees it. He's 23, he has the time to commit to it.
Edit: just saw the 4.6 40... that's going to be problem for a guy built like him. That's WELL off the mark for NFL players of his size