I played Soontir recently with PtL, and Stealth Device, thinking this should be good. Got one shotted by a B-wing that got too close before I got a shot off. Wrong place, wrong time. Just goes to show anything can happen.

If you play the same list (regardless of results) against the same opponents, their game should eventually adapt to overcome it. Be prepared for that sad day when no matter what you try, they've got a counter for it.

As for "is it fair?", I can't see any reason why not. It's not like you're trying some dubious tactic at all.