Sure, EU will be a weaker world power without GB. Maybe, GB will probably end up opening its borders without having a say in EU policy. Maybe there will be a lot of financial turmoil too in the next couple of years. And it is too bad that the people who will have to live with the consequences (> 25 years of age) of Brexit did not want it (74%). But to me, an outsider, Brexit was a big let down because of a different reason.
I believe that borders are petty, silly and to be done away with. I dream of a world without borders and I also understand that it will take many decades, maybe centuries for it to become possible. The idea of a continent full of countries who have fought wars for centuries coming together as one, was the best thing about EU. If traditional foes with centuries old rivalry could work together, maybe one day everyone in the world can too. That was the hope that EU fostered.
I read somewhere that there are only two angles that matter in storytelling – fear and hope. Unfortunately, fear seems to win over hope more often.