You can't hold Federer and Laver to the standard of another era because the conditions/situations weren't available. But there are some truth that you have to take into consideration. Fed doesn't get to play in a split fields, and he had to compete in a bigger pool. So if you want to compare title per title between Fed's era and Laver's era, Fed should have more weight. If you insist on they all have equal weight(e.g. Emerson 12 slams is equal to today's 12 slams), you are selling today's players short.
Wouldn't that be like saying the best soccer player in the English Premier League(EPL) can't consider be the better player than the best player in the USA Soccer League? With the EPL being a much bigger pool(and more countries) than the league in the USA, one has to consider(objectively) the player in EPL is a better player.