That's of course not necessarily true.
You haven't factored in the retardation of economic outcome that the present union is causing because it can only exist through the extreme and persistent application of force (which is very substantially regressive for human development). The reason they keep getting authoritarians century after century is because Russia as it presently stands should not exist, they can only hold it together with force. That comprehensive application of force destroys liberty, creativity, free expression, economic growth, investment, and so on.
You can simultaneously have economic negatives from the lack of a port, in a landlocked Russia spin-off state scenario, and be better off being out from under the forever strangulating authoritarian umbrella of big Russia. That is to say, that's just how horrific and dampening of human potential it is to be under the boot of authoritarian Russia.
There's a good reason so many nations that were formerly dominated by Russia are now exceeding them in GDP per capita.