Should I bother learning mid lane before going into ranked?

You should actually avoid Ranked until you've done at least 10000 matches in every single other mode including going 1v5 against Intermediate-Level Co-Op Bots in Custom-Mode.

Don't worry about mid.. like you said.. every.... wait..

there have been strange times where last pick got mid.. IDK... then again you can type in chat for someone else to mid...

I find that as long as you know how to support, adc, and jungle, you're good.

Most games seem to have a mid and top main, for some reason.

You main support eh? If you know how to play Annie then you'll do fine if you have to play mid. Just try a non-support build on her a few times in normals and you'll be set if you find yourself stuck in mid.

So far out of 70 matches this season, 2 I couldn't get Support; once I was Top and the other Mid.

Basically, however rare it might be, you'll eventually get stuck in that role you don't want. Try to have something lined up for it when you do. It could even be a flex pick like Lulu or Annie.

I am also a support main. After 90 ranked games, I have had to play another role about 25 times, most frequently jungle, followed by mid, then adc, then top. I specifically request support every game, but don't fight it if someone else insists.

I mid as heimer since he's the easiest in my opinion to play as a non-mid.