Id like to offer, they are, especially if you attack boost them (any big starship really helps, and the more the merrier), fortress killers (my favorite use for them!) if it doesn't have a counter sniper nearby. I've been able to use sniper ships (the full amount of tech 1-4) to in 2 volleys, drop a mark 2 and mark 3 fortress with minimal losses. (and a translocator helps if you have one to force it beyond its firing range and wormhole slide in fire, and jump them back out.) I lost maybe 12 snipers (as didn't see it had fired, taking nearly 30 seconds to reach them after it died firing, compared to 200-400 ships i would have trying to get it out of the protections it had (heavy beam cannons, flak, and others, given it was a tech 3 world)
I have noted they love to target shielded craft, making the riot starships a great way to soak up a volley to evac your snipers from the slaughter a fort can do. Move in snipers last, after a gate is clear, have them volley, pull them back out of the way, because i never lead in with the snipers, but bigger ships, the ai loves to toss in the arachnid startship killers, over a counter deployable. The longer you keep your own sniper fleet on your world, but drop in to use them for a volley, the better it goes.
At the same time, beware to heck and back if the ai is favoring teleport craft, it will, if they are on planet, zero in immediately on a chance to kill a few of them. (even if its going to lose 20-40 battlestations to kill 5 snipers.)
Raw damage, for sniper volleys, from tier 1-4 is a little over 1 million, a quick search, and you can boost to 5x, and 5 million points of damage every 60 seconds to a target that cant be healed, is staggering. Level 2 forts, drop, in a single volley, a minute, and you can kill a level on the second. you want to focus fire with snipers, if you want something to die now. Its hard to compare, but never lead in with them, since the ai has yet to remotely start building them with the way of sending them in afterwards, and pulling them out again.