Malcom's passage through Barça was so brief it's hard to truly value his contribution. Valverde never wanted him and, as such, never trusted him. The winger didn't even rack up 1,000 minutes and only scored four goals. No one can blame the Brazilian because he didn't have the chances any player needs to succeed. The problem, of course, was never Malcom but rather those who signed him despite knowing that he wasn't a player the coach wanted.
Fortunately, the terrible transfer was saved by an excellent sale to Zenit: €40m plus another €5m in add-ons. That's more than what he cost Barça a year ago. A smart piece of business which helps raise the money brought in through sales this summer, and there's still the futures of Coutinho and Rafinha to sort out. At least the club has learnt from its mistakes in the transfer market: they continue to (at times) to sign poorly, but they are selling much better.
Either way, this policy of signing players to later sell them on for profit shouldn't be something Barça actively searches to do. Making a profit by 'flipping' players is fine for clubs at lower levels who need extra sources of cash, but Barça can't create a budget based on sales. One thing which is very positive is that Barça have learnt - at last - how to sell players who don't fit into their squad. There was a period of time, not so long ago, where they essentially gave away those who didn't work out at the Camp Nou. These recent sales have actually helped fix the club's accounts.
At the end of the day, the priority at Barça is to sign the right players. Those signings should help the club win trophies, not make the accounts look better.