Canada is never considered INTERNATIONAL for US airlines if that transborder is the only segment outside the USA on your same day itinerary. And they never provide lounge access on such First Class bookings. It is one's Elite or SE status [STARGold] where transborder is considered by US and UA to be INTERNATIONAL, and thus lounge access is granted. So US was correct not to permit access on your itinerary even if your family was in First Class.

US First Class is an elite perk, and the service reflects that. US makes little incremental income from the cabin and seldom sells real First Class seats domestically, unlike AC which still makes money selling its front cabin and keeping upgrades limited to high fare travellers.

YOWkid, I think you got access to the MLL because AC/UA recognize their transborder services as having lounge access when traveling into or from Canada, but not onward. So if you had a segment from the US gateway to another US city, unless you were Elite or a non-UA/US STARGold, you would not get RCC access. And I don't believe UA operates any RCCs in Canada.

As for your other complaints or comments, that's the reality of US domestic service. US has dropped its fares to compete with SOUTHWEST, and adds the extra benefit for its elites of the front cabin upgrade. To keep costs in line, meals are whatever is being offered in the back, gratis as you note, and drinks are free. Otherwise, don't expect what you get up here...