As someone who uses Raids occasionally but very rarely unlocks higher marks, I see it as a perception issue.
Raids are single target killers, they are not general combatants and do poorly if they do not have right-click direct targets.
So, do you ignore the AI ships and nuke the guard posts and command station and then tank the freed threat on your static defenses? Raids are great for this, but the guard posts changes are a giant nerf to this playstyle. This playstyle is also where raid IIs or IIIs got unlocked most likely as raids see heavy use playing like this. OMG! My raids are useless now!
Or, do you clean out the AI's fleet ship defenders as you clear out their guard posts using your fleet blob, only breaking out the raids for raiding high value targets such as a data center or raid engine? Raids are excellent at this also, but they do not target the buffed guard posts so their effectiveness is pretty similar to what they were before the guard post buffs. This playstyle will almost never unlock higher Mk raids as they are not one of the players primary attacks and the raids only get used a few times a game so that 4K knowledge is better spent on other things. Hmmm, my raids are not quite as good as they used to be, but they are still doing pretty good.
The other consideration to unlocking higher Mk raids is that if the target dies, anything beyond that is wasted. The number of situations where a cap of Raid Is would fail to destroy their target but higher mark Raids would succeed is very low. If there is something that would prevent Raid Is from killing the target (gravity, high level defenses, etc.), that same thing would probably prevent Raid II & IIIs from destroying the target.
D