I think you're mischaracterizing the situation.
Perspective 1: UK is breaking up with the EU, not vice-versa.
P2: EU gets some adv/dis-advantages by including UK specifically P3: UK had some advantages/disadvantages from being part of EU P4: EU has incentive outside of British sitch to stay unified
My (american) perspective is that Britain should stay in the EU because while their direct adv to leave may outweigh direct disadv to stay, they are subject to P4, which is to make an example of someone who leaves.
Exclude your judgement of right, wrong, and what should be. Look simply at leverage.