Its deep sub and is needed for control which is the job of sub talent tree. Two mages could do the same. I can imagine you have been ganked by a rogue and it is a traumatic event for you. Many hate paladins because they can lay of hands bubble etc and win no matter what depending on what cooldown is up. Yet I dont scream bloody murder because its part of their design. Sapping and controling the field is the whole part of sub rogue and rogue in general.
Sap It is useful in pve and pvp. As a paladin you got spell breaker stuff as prot. A lot of great quality of life additions for all trees. Rogues waited all beta and got paid dust, now you scream foul play and havent even seen this in action. Roll on a pve because there is always a new flavour of the month and if it bothers you that much well that doesnt sound fun.