Osman is a great commander for new players who do not have nuking legendary commanders especially for new servers in Rise Of Kingdoms. Osman Talent Tree is bad for field fights so you will usually use him as a secondary commander.
Osman is a great commander for new kingdoms but later he will lose value. Why? A lot of people will get a nuking commander that can do an insane amount of damage like G.Khan and they will focus you. Osman does not have any defensive skills and you will die insanely fast. So that is why I would not recommend using him on old servers.
In the early stage of the game, you can use him for a rally to, he will prefer good.
From skills, you can see that he is all about nuking so pair him with a commander that will provide nuking and rage generation
When you are fighting on-field try not to get focused while using Osman or you will die fast.
Good Pairing options for Osman are:
He will bring some Survivability and rage generation. great pair for new kingdoms.
Also pair that will have nuking and rage generation. But be careful, you can die fast.