as woobie said, the argument it self is pretty pointless. of course Messi is better but the football has changed alot, training facilities have become better, trainers know better etcetc.
we can however both agree on the fact that the players were the best of their generations at their peaks.
For me the biggest difference between the 80s and today, is the fact that the game today is much more global. During the Maradonna era, teams had 2 or 3 foreigners, and the rest were natives. That simply meant that football in general was probably (surely I would claim) inferior in those days.
Nowadays, clubs can pick and choose players from all over the world, to suit their needs, and tailored-made for each and every position (pacy full-backs from Brazil, athletic Africans for the DM position, a talented Latino for the AM position, and so on and so forth) During the 80s, the top national sides would be of a higher quality than the top clubs, today it is the exact opposite.
So this fact for me, tilts the argument decidedly to Leo's favor...