IIRC, snipers have a relatively low retreat range because they're faster, whereas sniper guardians have a relatively high retreat range (15000 or so?) because they're significantly slower. The additional problem with using lasers is that there are just plain more AI ships in range, so not only are you disabling their engines about four times as (fires half as fast, 3/4 the engine damage with an engine damage cap that's 50% higher than machine guns so a little less than twice as many shots to hit that engine damage cap), you'll probably have twice as many targets in range at any given time so getting around to disabling the sniper engines is going to be an absolute pain because you'll take 8 times as long disabling the engines of everything in range.
