The bottom line here is that OP chose to fly a connection between SEA (Northwest of US) to LGA (Northeasy of US) via DAL (South) rather than B6, AA, or DL, all of which offer nonstop service.

OP's rant about fuel xDAL points to a simple lack of understanding. If too much fuel is onboard for the projected route, the aircraft must hold while it burns fuel prior to landing. If the delay is not known at the time of departure, it is a waste of time and money as well as a poor environmental choice to circle LGA for an hour or two,

OP's ultimate point regarding AS's base is, of course, correct. That won't change. AS flies TCON, but it does not have a full route network and thus LGA and other East Coast airports are and always be outstations. This is especilly true of LGA and DCA, both of which are slot-controlled, meaning that some other carrier must drop a rotation before AS can even think about picking one up.