While i can see most of your points aside the
being skillful (im guessing that was just a joke)
I agree with the point of duskblade being most of the cause of it, but i dont believe its whole reason.
For example if you removed duskblade then just about every ad assassin is basically weak. The reason they gave a strong braindead item like dusk is because most ad assassins have alot more counterplay than ap assassins (not all just most) for example while most ap assassins can pop enemies extremely quickly they also dont have much outplay potential which makes them viable whether they are braindead or not, while ad assassins have alot more outplay potential (whether its because their burst isnt as fast because they can aa for dmg or because their burst is extremely telegraphed)
Zed without dusk is relatively weak because his ult is countered by stopwatch or hourglass and without dusk he doesnt quite have the dmg to pop people in one combo
Talon without dusk isnt able to pop people and his burst is at some points easily telegraphed
The rest i assume you can figure out on your own.
My point is that there is too much outplay potential in champs now, so in order to make assassins viable they need to give them the ability to assassinate.
I dont think ad assassins are a problem right now, if anything its ap assassins that need a nerf. If you look at the most played champs from plat+ the first assassin that appears is Ahri at number 23 and there are 4 more ap assassins after until the first ad assassin which is zed at 43.
I do wish there was a way for them to fix the braindead part about assassins because i honestly loved assassins being skillful to play. But i think if they remove it then ad assassins will be in a very bad spot.