I'm no SWA sunshine pumper, but this is all a bit of hyperbole.
1. 73 for the rest of your life? "Like anyone can even know that." We have no idea what's going on tomorrow in this company, so it's a pretty bold statement that we'll be flying the 73 for the next 30 years (assuming you're ~35 years old now). I'd put a round of Boilermakers on us having a different airplane in the fleet in the next 30 years.
2. Multi-leg days? Sure. I don't know many guys/gals that do 1 leg a day, no matter the airline. And if you do, it's probably a long leg. I'd guess the duty days are about the same. Give me three 1.5 hour legs over one 7 hour leg, but that's just me. I've had plenty of trips with only one leg in a day.
3. Same towns? Doesn't every airline fly to the same towns? We have ~120 destinations and no one has added more in the past year than we have. If you think SWA isn't going to grow even more in the future than I don't know what to tell you.
When looking at seniority, it really means jack shit if you can't hold the base you want to hold. Looking at retirements only tells part of the story. Can you upgrade faster at AA vs. SW? More than likely. But I'm assuming you'll be stuck in NY or MIA or whatever the junior CA bases are at AA. Just like you'll be stuck at OAK or LAX if you upgrade at SW.
SWA isn't a bad place to work. Yes, it's all narrow body flying and that's not for everyone, but as a Herk guy who has a 3.0 ass, it's just like flying in the desert. Except no one is shooting at you and the loadmasters look better (sometimes). Only having one aircraft in the fleet is good and bad. As previously stated, if you want to fly something else, you can't (for now). At the same time, if I want to trade away a trip, I have roughly 4500 other FOs as trade partners. I can pick up extra flying as a reserve holder and even trade my reserve for a trip if someone is willing (supposedly most airlines don't have this option). 99% of the CAs I've flown with have been really great dudes that generally don't give a shit about how you fly as long as you get us there safely.
On the other hand, the ra-ra OnE LuV shit is wearing off. We're all "one team, one heart" until they threaten furloughs 2 weeks before Christmas, knowing they had no intentions of actually following through with them. One thing that came out of it is our pilot group and Union are stronger than ever (this coming from the mouths of the old guys). The company thinks pilots will choose to come here versus others because we treat our pilots better and "we've never furloughed!" but that's all now bullshit. We get paid less per hour and we generally work harder.
I'd advise anyone to do homework and pick an airline that fits your lifestyle. Also look at seniority at your desired base, not just company wide.