Wouldn't worry too much about overall comp synergy within reason until high diamond and even then it's still kinda whatever in solo/duo.
After enough games with whatever champs you're considering, you'll get a feel for when you really hate playing X against their Y, or when you really like playing it, and then you can pick based on that. If theres no major influences that jump to mind, reasonable to default to whatever you have the highest win rate on (after all, many people basically one trick to diamond). If you're really good at a champ, you can generally handle things even if the enemy has a 'counter', unless the person playing the counter also happens to be really good at that champ which isn't something to expect until you get really high.
If you're feeling particularly analytical you can figure out loosely if your comp is looking to force fights or sit back and poke or have someone split push while you wave clear at which point you could pick based on that, but with solo/duo being disorganised as it is, sometimes people won't play to overall comps strengths anyway so it doesn't matter too much.
There might be something to be said about the overall scaling of early/mid/late, where you may want to help bridge some gaps (so someone is strong at every point in the game), or go all in on a comp that spikes at the same time. It's probably a matter of taste for which route might be 'better', and really I feel like it comes down to team synergy/playstyles for which is better, and you can't really know that with the randoms of solo/duo.
There might be utility in learning an AD mid laner if you find yourself in a situation where your team is super magic damage heavy otherwise, but out of what you mentioned I'd probably just pick based on your own personal expectations surrounding the match ups rather than picking as part of the overall comp.
