I'm not saying they should or shouldn't because clearly you keep someone like Oliver. But this is only in a situation where Oliver and Merrett both want out. Remember, Melbourne's age demographic should very much see them challenging now and Merrett very much fills a need for their list.There is absolutely no way Melbourne should swap Oliver for Merrett lol...
Despite his obvious flaws, Oliver is still a top 3 inside mid at clearances/contested possessions, whereas Merrett isn't even a top 15 midfielder in the comp.
Melbourne will be fine on the inside without Oliver as they still have the likes of Petrecca, Viney, Brayshaw and Harmes. His value to each club depends on needs. Teams like GWS, Geelong, Brisbane, Port and Bulldogs don't really need Oliver as much as Merrett because they already have a good stock of inside mids. For teams like Essendon, St Kilda, Hawthorn and Sydney, Oliver is a much bigger need than Merrett.