a) It's totally fair to have a 5 vs a "non" 5 as long as both teams have the same number of people. I used this 5 agaisnt non 5 because: if it's fair in the worst case, it's fair in every other case. It's just an excuse to say it's not fair.
Odds really are just that: odds. If you take odds into consideration then the enemy team has the same odds as you since the enemy team has the same odds as you to find a x man premade against a team of full solo players so it's still fair, wanna only use your specific point of view? The odds won't change: that 1/5 solo player has the same odds of being both worse or better than you, so it's still completely fair. You can't have an argument when you say "I have more odds to have a bad player" but don't take into account that you have the same odds that that player is better than you. So: your argument is valid only when the odds that that player is worse than you/enemy are higher/smaller than the odds that that player is better than you/your enemy, which is not the case here.
b) Nope, my point is not false since they don't say that premades have an advantage, they don't have any, like I already said: premades don't give you more ad, as, ap, ar, mr, ms, hp, mana, whatever, so they have no advantage, they are exactly as strong as you would be with the same runes/masteries/champ. They want to adjust the system because they have an "indirect advantage", which is simply that solo players tend to not trust each other, but it's not a fault of the system or of riot, it's the players who just think they're perfect and everyone else drags them down so they make a fault of of the system and say that riot is full of incompetents, so riot has to work around that even if they could just say: if you can't play in a team it's your problem, not mine, but if they wee to do so most casual players wouldn't play the game so they have to accept this compromise,
Also there are people who really can't prioritize anything else over queue times: they have jobs, families, problems, so they can only play for 1-2 hours a day, if queue were too long they wouldn't be able to play at all, so queue times are incredibly important in a game.