In the early 80's, a certain striker from the dark side scored 49 goals in a season in all competitions, so would it not be better for you to compare Messi's goalscoring prowess to Ian Rush, who scored a similar number of goals to Messi, rather than probably the most prolific centre forward to have graced English football.
I'm not saying for one minute that the Welsh Pinocchio was ever in the same league as Messi in terms of overall ability, but if we are comparing goalscoring records alone, then surely he would be a far more suitable candidate for comparison. My point being that Rush's 49 goal season was only 30 odd years ago and is pretty much forgotten. Dixie's 60 league goals were scored 80 odd years ago & are still talked about. I think this highlights what an achievement it was.
We could go on all day debating whether or not it was easier to score goals in any particular era, but the fact is that the players of that generation were not given anywhere near the same level of protection as modern day players. The game may not have been as fast, or as tactical as it is today, but players went in hard and didn't roll around the floor like they'd been poleaxed every time a defender went within five yards of them. How many of Messi's goals have been scored as a result of defenders being weary of getting too tight to him knowing that he's going to go down like a sack of shite as soon as they breathe on him. Different eras, different game, but to belittle the achievement of scoring 60 LEAGUE goals in a season is just spouting utter shite!