I admit that the Ottoman ideas are strong, but each country has it's strong points in terms of ideas, which define one's strategy. Byzantium has theirs.And you neglect to mention the OP Ottoman ideas (more than make up for the 25% manpower boost) plus the instant Empire rank and free culture conversion and adm costs.
The thing is, it's not a fair comparison. You were comparing the decisions against each other, and your reasoning should be ceteris paribus.