200 characters sounds a bit excessive to me. What are the chances of a typo while trying to enter your password, just to generate the private key?
My suggestion, if you wish to use a secure enough password, is first to make sure you are not largely using actual words or phrases. Certainly, use information only you know, organized in a way only you could reconstruct readily and consistently. I'd keep the length under 100 characters, so as to minimize the chances of persistent typos.
A random private key would still be mathematically more secure, but the chances of loss may be higher if you have difficulty securing and protecting it. How many people have "lost" Bitcoin because they forgot the password to their wallet, or the wallet was uninstalled? How many people have had their Bitcoin stolen because copies of the keys were stored in an unsecure fashion or location?
You really need to find your risk tolerance on both sides. Do you want something less cryptographically secure but more easily recoverable (lower chance of loss, higher chance of theft), or more cryptographically secure and less easily recoverable (higher chance of loss, lower chance of theft)?
I personally lean toward making a brainwallet password which is secure enough to protect my Bitcoin for the length of my lifetime (or longer, if possible), rather than use a piece of wallet software where I might lose the private keys if my hard drive fails, or where copies of the private keys may be more readily stolen because I couldn't keep them secure enough.