Not necessarily, there are better adcs for different comps.
Need some utility or lockdown for teamfights?
or
Need an adc that can self-peel or stay safe in teamfights?
Need an adc for a duel/pick comp?

You may have success with Quinn due to her overloaded duel kit that allows her to win and dive players that get caught out (especially good in lower ranks), but that doesn't mean she is the best choice.
As for synergy, you are sorta correct. Any bot lane can work, or you can expand that to say any champion in any lane can work. It all depends on matchup/player skill/team comps/ etc. Hell, Dyrus went Tank Nami top (yes,
) and won a ranked match in high elo (diamond or master? Idk).
The point is, it's really up to the adc to at least suggest who would be better suited for their playstyle.
They play an agressive, dive-orientated style but the team needs a tank or someone to peel?

They play a safe, farm-fest style (so needs a champion that can zone/trade by themselves) and the team needs some poke/siege potential?

ADC is extremely passive and the team requires sustain for their competent front-liners for long brawls/fights?

As you can see, there are optimal picks that are simply better than the others. Your adc also knows who they work with best on a player-skill level and not just champions, so it is wise to at least consider to their requests.
P.S.- There are comps that simply don't work. Don't go
/
into
/
. No amount of synergy can save that poor rat if the enemy is at least slightly good.