I wouldn't mind these situations if there were staggered reward punishments for going in as a group. Like, gaining less lp when in premades and not being punished the same when running against solo players as you would in premades. Like an lp handicap.
For example: I join solo and get a certain amount of lp from my game.
I join the same game scenario, but as a premade and make less lp from that game in relation to how many people are in my premade.
I queue up solo and lose against a group of other solo queue players. I receive my defeat.
I queue up solo against a premade group and lose, but face less of a punishment for that loss due to my handicap.
I queue up in a premade and lose, facing a harsher penalty because we had the advantage as a premade.
I queue up as a premade and win, but gain less lp because the opposing team had a handicap due to mostly solo players in arrangement.
This handicap system would make making premades safer, but take longer to climb the ladder. Consequently, solo players who can properly support or carry their team are rewarded for playing well and climb faster, but will still have to face the safer premade teams.
I will make this clear:
Solo queue players should not be punished for preferring to queue up solo.
Solo queue players should be rewarded for going against a slanted system skewed in favor of advantages gained from outside the game such as voice comms and teammates who have generally played and practiced together before. Solo queues should have an lp increase just for going in solo. A team of solo players are always at a disadvantage and winning in this scenario should grant them a greater reward.
I'd even go so far as to say that Premade Promo wins are worth half as much as Solo promo wins.
Solo games should give greater reward in relation to risk of loss, where as safer premades should climb slower because it is based less on individual skill and more on team coordination.
Look at TSM. Individually strong players with poor communication can routinely flounder. However, weaker individuals with good synergy can still succeed despite poor individual mechanics.