There is nothing wrong with Extruded aluminum anyways, as long as its heat treated properly afterwords.
Extruding is the same as forging, as in it reduces the amount of material you need to machine away later. Aluminum ladders for example, need to have lots of strength and not much weight. Most of the parts are maybe 1/16th of an inch thick and can have the weight of a BIG human moving around on it with no issues.
Aluminum gets MOST (like 80% IIRC) of its strength from the T6 heat treatment process, weather its Billet, forging or extruding, or even if it was injection cast (although 7075 is not good for casting, too thick... most cast aluminum has silicon in it to aid in flowing into the mold, which also weakens it) as long as heat treatment is done its going to be JUST as strong as a forged receiver, but they use less material.
Aluminum is not like steel - which depends greatly on the granular structure of the metal - Aluminum gets its strength from heat treating, so wherever all this "extruded = junk" came from, is exactly that. Junk.
ETA
the proof is in the pudding, since the SCAR has extruded Aluminum receiver too, and is doing great in all the endurance trials its run though.