It's all relative. You could have 2 rounds or 50 rounds and you would still need to replace the same number of players at the major league level. The average roster player is going to take up 7 or 8 years of service time in the bigs. This means you need to draft 1/7th or 1/8th of a roster every year, which on a 25-man roster, comes to about 1 in 3 or 4. Now of those 3 or 4, you get a lot of marginal players, who didnt even make it with their initial clubs and get bounced to a few organizations, but still fill up some of those roster spots at the ML level. So really, you should expect to get 2 average starters in a few years in a draft. Someone like Corey Hart is worth about 1.5 league-average starters in trade (Prince could net 3). So you draft him, and get a marginal scrub that makes it in 5 years and another that latches onto another team and wins a roster spot, and you've gotten a respectable draft. Obviously you can debate the weightings of the numbers and years that are equivalent, but the same concept is there.