now with 1.8 pvp you don't have to be as careful with the timing of your hits so if someone's jumping you can easily hit them and with 1.8 having much more knockback (especially while in mid-air) jumping is a really bad idea if you're trying to get as many hits in as possible.
That's the thing isn't it? A player who knows what he/she is doing can use this to their advantage. BUT their are multiple scenarios. Either the player you are playing against just jumps around constantly and all, that kind of player you can easily hit. A player who knows how to get crits in
and avoid getting hit makes the whole concept of critical useful. Although I don't have any video or of such, I have had some intense matches against people who know how to get crits in and still pvp great. For example, you might want to come to 1.8 FFA and hopefully look for SorryNoTortilla, or occasionally BlockMasterFC. They know what they are doing.
But now on to other small advantages you can take of the map itself. The maps are not completely flat. In fact, they are really hilly and such (which in my opinion is a nuisance). For example in Savanna (FFA) although it has a lot of flat land (good for pvp), it rises occasionally. If you were chasing someone, time your hits (because timing is also important).
Or if you were using crits at close range, the player most likely won't be knocked back to far giving you an advantage. Overall my point... critical are important.