Counter Picks and Champ Select don't matter for SoloQ

They really don't until plat+.

Yes, getting counter picked may make your lane harder, but typically, people who are lower than plat do not fully know how to take advantage of these circumstances. I used to play a fair bit of tournament chess and would always obsess over the opening or the first few moves of the game which is basically very similar to champ select in LoL, as which opening you play in chess determines what win conditions you are going for and there are certain counters to certain openings. But the thing is, when you aren't a grand master or master or expert at chess (basically plat+), you aren't really going to know how to take advantage of an inferior opening. Sometimes, playing an inferior opening gives you the element of surprise, as nobody knows how to play against it. Sometimes, in LoL, it is better to pick a non-meta champion that you know well, than pick a super meta "OP" champion. And if you do get counter picked, if they do not know how to take advantage of the counter pick, then it doesn't matter right? In league a person might outplay you during the laning phase, but if they don't know how to snowball it, why does it matter? In League matches, you always have late game, and team fights to get back in the game. Unless your opponent snowballs their lead so hard that you can't team fight or split push, the game is still winnable.

This is why people advise you have a few mains that you are really good at, so that it doesn't matter whether or not you get counter picked, you can still do well as eventually you will need to learn how to play against counter picks.