Surely most people realise that, without management interventions, all eutrophic wetlands will eventually revert to woodland via scrub, pioneer woodland (usually Birch and Willow) and then, through progressive drying out via transpiration and litter accumulation, to climax woodland.
While I agree that, in the interests of diversity, it is good that some reserves are allowed to pursue this trajectory one size does not fit all. If you want to retain diverse healthy, nutrient-rich wetlands they need to be managed. This has always been the case - e.g. the traditional reed cutting for thatch in the Norfolk Broads (which were originally created by generations of peat-digging) .