He's not fighting against closed systems because they are closed. He's not fighting against closed systems in general for any reason. If he was doing this, then you would have a point. He is angry that the status quo of having an actively supported open Windows platform is being threatened. He is fighting against losing that. The new closed system is just the evil actor that he identified.
This is a classical case of loss aversion. [1] Tim would be at least equally mad if Microsoft decided to redirect all its efforts from win32 to cow milking. Would you then claim that Tim is a hypocrite for having drunk milk instead of actively boycotting the dairy industry?
Yes, you could make the argument that extremely black & white attitude is necessary, and that if you like some open system then thus follows that you need to fight against every closed system. Some people like Richard Stallman do this. However most people, like Tim, belive that a more gray world can exist, and tend to fight when visible threats manifest and otherwise spend their time on other things.
There's no gain to society from having an open platform (I can develop Windows apps for free only having Windows), and converting it to a closed one.
The transition of users from computers to closed devices like tablets and phones means now most people are only consumers and can't create anything on their devices. Except for selfies, that is.
All PC platforms should be actively protected from this closure.
If you think only a GPL OS deserves to keep that openness then you are ignoring the 98% of computers that don't run Linux, for IMO silly ideological reasons.
If he is such a knight of openess, then Epic should only have targeted open platforms.
Yet they happily took the money those bad closed platforms brought them.
It is not a matter of consoles always being closed, rather a duality of principles when money speaks.