The two positions are not mutually exclusive. Most capitalist interests favour remain to smooth the flow of capital, but if brexit happens, while certain possibilities that they would like may be closed down, others open up. As is often mentioned here, the post-war settlement both in the UK and elsewhere in Europe was in large part an accommodation of capital with the interests of workers in order to preserve capital - concessions granted if not willingly then with a view to maintaining supremacy (that it was predominantly loss-making industries that were nationalised being a case in point). Concessions such as those granted in EU worker legislation could be seen in the same light. But take away the framework in which those concessions were granted, and capitalists may no longer see it as in their interests not to scrape away at them.
A fair few people on here, me included, have never argued that the EU is anything other than a neoliberal project. We have merely argued that the EU neoliberal project is not the worst of all possible worlds. Change the structures, and things can get even worse.