The only good way to use a rift in PvP is to lock down lanes from the safety of a corner, making it much easier to win duels since you have either a constant (though painfully slow) heal or a more powerful shot. You could try to use it offensively however unless it is a freezing rift with the specific Stasis Aspect since more often than not you will be killed due to the casting animation locking you in. It would be nice if there was more Damage Resistance or a faster heal/overshield however it probably would be much less fun to play against, as once you have that corner set up then it would be hard to counter for the next 15 seconds.