Essentially there is one huge disadvantage to dual queuing - which is that your team gets an ELO penalty compared to the other team.
In other words if the opposing team does not also have a duo then they will be individually more skilled than your team.
In order to make duo worth it you need to bring advantages to the table that outweigh that penalty. This means that you need superior teamwork, game knowledge, and ability - not just for your lane but for the whole game.
So duo bot makes sense in terms of winning that lane. You are (or should be) on voice comms together. You are (or should be) used to working together and know how to get that synergy you need to dominate in lane.
But the price of that is both the other lanes potentially being outmatched. You've traded one winning lane for 2 losing ones. Unless you are able to take your bot lane and really dominate, start taking dragons, roaming to mid, etc, then your team as a whole has lost out.
Doing mid or top+jungler is actually a fairly strong duo combination as well. You can work nicely co-ordinating ganks or invasions. But you still have the same problem, you've gained in one lane to lose in two others.
If you go top+mid, that's even worse as now you're extra co-ordination is really weak in the early game. It can work but only if you both start roaming early.
So that's the trade-off with going duo queue. It's not enough to win your lane. You need to use the extra co-ordination between the two of you to win the whole map. For example a successful jungle+mid will:
Steal an enemy buff, defend own buffs, ward map and invade on enemy jungler. As soon as you hit 6 you'll both move together to do a 4 man gank on enemy bot lane then take dragon, etc.
You need to get your team ahead, not just yourselves.