"Hurr durr, in the old days everyone had to know offroles because of pick order"

Yeah? Well guess what smartass? Before role selection, being forced to play an offrole like support because you were last pick was not an infrequent occurrence, this could happen several games in a row if you were unlucky enough. Which means you had plenty of practice offroleing.

Now compare that to the current autofill system, assuming you get autofilled into ONLY support(which isn't realistic; getting autofilled into top or jungle isn't uncommon), you're looking at getting that autofilled offrole around 10% of the time. This is NOT sufficient practice to be playing that role at a comparable level to your main roles for the average player, ESPECIALLY at higher elos where the enemy will abuse the absolute shit out of you if you're not up to their level in that role.

tl;dr current ranked system encourages you to master 2 offroles to climb as efficiently as possible but then throws that on it's head with autofill by putting you into a role you cannot practice because you rarely play it