I don't 'knowledge raid' very often, but when I do, I send a pretty substantial force. Ever since I built a large number of raid starships, I also tend to (while I'm there) sweep the system clean of guard posts.
So, I don't think the mechanic is either too hard or too easy, but it does tend to get tedious when you're closer to the end and just want to blow up that last AI homeworld already but really need just a few hundred extra ships. If anything, I'd be in favor of some sort of high cost "remote knowledge gathering" mechanic, but I don't particularly see how it would make any sense from a thematic standpoint (poke a stick through the wormhole?)