True, it can cause for a huge gap in skill between certain lane matchups, but given the overall spread, the player placed at a disadvantage individually should have advantages elsewhere despite his own lane.
The teams are paired up according to the team's overall mmr. If you have a low elo player queuing up with a higher elo player, it makes sense that the average elo of the opposing team would sit somewhere in between.
I guess what I'm trying to highlight is that the disparity you're referring to should only be apparently on an individual level. If you take a step back and view the team as a whole, it would appear more balanced. For example, while there was a Bronze against a Plat in one lane which would go in favor of the Plat's team, the Bronze's team might have two Gold players going against Silver's or Bronze which would have two lanes going in favor of the Bronze's team, giving a contribution possibly equal to or greater than the contribution the Plat player brought to his team.
So, in the big picture, the overall spread can indeed be relevant. Rather then deny to players from duo queuing together, they compensate the disadvantaged party with a possibly stronger overall comp.
I've had my fair share of experience with it as well. Going against a Diamond V Kat top lane as a Bronze I Akali S3, and got my pride handed to me on a platter and it sucked. But we ended up winning due to the advantage other lanes had.