Most of those $200M in fees are Ethereum gas fees that are being burnt on-chain. Those aren't income for OpenSea, they're costs incurred by all parties as part of doing business.
On average, you should assume that OpenSea takes around 30-40% from this 200M fees.
Opensea takes a % fee, and the seller takes a % fee. Can you prove it's also including gas fees?
Otherwise they wouldn't trade.