it's definitely hard to determine at which point the use of HGH is simply to fix a medical issue, and when it goes past that to give an advantage. Without a clone of Messi to compare we will never really know, if that makes sense. I mentioned Bradley Wiggins as it turns out he had a long term TUE for an asthma medication, which is a steroid which aids breathing. The issue with Wiggins is, that drug would benefit someone who didn't have asthma, and he was taking it preemptive to any conditions surfacing, it's a really tricky thing to deal with and Russia have made complaints regarding TUE's being handed out favorably to certain athletes/countries.
Dozens of Russian athletes have been caught using a drug called Melodonium, Sharpiniova the tennis player got a 1-2 year ban for having it in her system, the same as Povetkin, a heavyweight boxer. Melodonium is a medication given to people to aid blood flow, this obviously also increases athletic performance, so we had dozens of Russian atheletes who convieniently all developed conditions which needed treatment for Melodonium
I am not saying Messi's case is similar to this as he took it when he was growing up, I am just trying to explain there is a thin line between therapeutic use and performance enhancement, and unfortunately with some drugs you can't really have one without the other. But the issue is, how did whoever medic who treated Messi know at which point the HGH took him past what would have been 'normal' for his genetics, there is no way they could have known what his natural height should be, for all we know with normal growth hormone Messi may have been more like 5'6-5'6 (around his dad's height), and got an extra 2 inches artificially.
His strength on the ball and ability to twist and change direction at such speeds are pretty much unique to him, in the way we haven't really seen another footballer who can change direction at such speed, Messi is incredible to watch and he makes it look so natural. Ronaldo is incredible, and being a man united fan I obviously have a bit of loyalty to him, but Ronaldo looks like he tries so hard, Messi just looks like he was born to do it.
I don't think anyone can really say for certain whether or not HGH benefited Messi past the point at which it became an unfair advantage, no one can claim Messi is a cheat, but no one can say his abilities are 100% natural either. If Messi was born in the 1950s and hit age 20 in the 1970s, HGH would not have been readily available so he probably would not have been a professional footballer due to his height, Ronaldo would still have been a great.
So im my opinion, is Messi an intentional cheat? Absolutely not, but he has had an artificial aid that other people are not allowed.