Trade deals take so long because they can, Lawyers love sitting on their butts being paid to dot every i and cross every T.  Two people (or countries) in a room can come to an agreement fairly quickly, twelve not so quickly. Plus when was the last time you saw any government do even the simplest task in an expeditious manner.
Trumps point seems to be a collection of bilateral trade deals only with countries that will benefit not just themselves but also the US.  I think his point actually makes a lot of sense, at least from the point of view of the US.