"At least" being the key qualifier here. There seems to be an assumption that the next Cubs core already exists and is just a few years away, but there is no guarantee of their current prospects materializing into anything. There are a lot of intriguing prospects in the system, but certainly no sure things. If the only realistic path to building a winning team is to start with a core of young, team-controlled players, and if the Cubs current group of prospects doesn't develop into that core, then we're in for an extremely long period of mediocrity. With Happ being one of the few players on the major league roster who can bring talent to supplement the current prospect pool, trading him should absolutely be on the table, and sooner than later.