I kind of agree with this but not really. I saw a good video on youtube once about it but I cant find it. Something along the lines of:
Everyone takes their idea of meta picks from watching the competitive scene (basically)
Some of these picks are good because something changed to make them good
Some are good because they are FOTM and no has figured out a counter on the pro scene yet
Some are good because their 5v5 potential in the competitive scene is great.
What it comes down to is that anywhere below plat level play, (which is like 90% of people I think?) champion "viability" is not really a thing. There's no way that your average solo Q team has the level of team play and coordination that a pro team does. It mostly comes down to, how well do you know the champ you are playing? and how well do you know the matchup? Even at higher levels this is kindof true, there is a korean streamer who plays only GP I think? and hes like D1 to challenger level.
Point is that basically champs are considered weak if they dont show up in the pro scene. And this idea is pretty flawed.
On the other side of the coin, you have certain reasons why non-meta champs could be considered weaker.
If you watched the spring split for season 3 LCS in NA or EU regularly, you would have a way deeper understanding of champions like renekton or shyv than you would of maokai or swain. Because of this reason alone, if you pick a champ that you are good at but your team never sees, they might not really understand how they work and therefor will find it harder to play with you.
Case and point I played a game with my friends as Galio mid, I used to play a ton of galio support and mid so I knew his kit inside out. My friend was the jungler and came for a gank and said "Galio has a taunt right? Can you taunt him?" so I flashed and ulted, thus taunting the enemy ziggs. My ult ran its course with my friend still waiting. After it channeled and I asked why didnt you come, my friend responded with "Oh, is that his taunt?."
tl;dr Meta comes from the competitive scene, people wont understand non meta picks as well, doesnt mean they are bad, just that less people know how to play with them.