Noni Madueke's arrival wasn't to replace Saka, but rather as a backup player to ease Saka's burden and fill in for him when he's injured.
I don’t think anyone will even think Madueke will replace saka, what is Madueke playing that will make him replace saka, which player will Arsenal even be signing that will replace saka for now? I don’t think there is any player, Madueke is just a backup player, and am sure they won’t be using saka frequently again, matches which they known that it won’t really be difficult for them, am sure they will bench saka and use Madueke, or maybe when Arsenal are already winning confidently, then they will bring Madueke into the match.
The main purpose of Madueke’s signing is not to replace Saka as you say but to offer support as a backup for Saka next season. If you followed Arsenal progress last season you would have observed how they struggled when Saka incurred an injury late into the season resulting in many draws. Arteta is out to change such situations for the coming season. This is a good move in my opinion and I am excited the deal is happening!