I think Arsenal wouldn't be a perfect place for Rodrigo because Arsenal already has good wingers, and if they sign another winger the it would be hard for them to used Rodrigo in X11 sheet.
I must disagree with you on this point... Martinelli has been quite ineffective on the LW for the past two seasons, while Trossard has been injury-prone and can't really play a lot of minutes... It's worth noting that Arsenal signed Madueke as a backup for Saka, but the fact that he already has a lot of minutes on the LW clearly shows Arsenal needs someone like Rodrygo
[the main issue is, I don't think Arsenal can afford to sign someone with that kind of price tag (at this stage of the transfer window)].
While Rodrygo is a right winger, who plays at the same position as Saka, there is still something I do agree with there, Rodrygo could still be a better left winger than Martinelli .Which Arsenal would love to do, but you also need to think about your finances.
Let's say you paid a ton of money and got Rodrygo somehow, not even sure if that will be possible but lets say that Arsenal did actually get him, how much do you think they will pay Real Madrid? They will need to pay a huge huge sum to them, and that would mean Rodrygo will want more too. This causes a lot of trouble, isn't it better to spend that on 3 different players and make the team better, instead of spending on a single player and make the team imbalance on how much they spend?