Sure your team comp is important, but youre a silver V (low elo). Do you know this person from several games or is it a random match? Do you know who else they have purchased?
I have a silver account I never leveled up due to lack of interest with probably 15 boring ass champs.
I have a bronze account I have never leveled up with almost all champs unlocked.
I have 3 gold accounts with almost all champs unlocked.
When you ban someone they want to play, you are risking banning their main champ who they know how to play. They may hardly have any other rune pages. Now if they are jungle, and they want to take soraka, by all means ban that shitt. But your bans should primarily focus on people you dont want to have to fight against. I.e If I take pantheon top I can beat EVERY meta top laner, except volibear at my elo. So I would ban volibear. Rather than waste my time banning someone who my team wants to play.