Who pays?

Southwest points redemption cost is proprotional to Southwest money ticket cost, so on paid Southwest flights you get a fairly fixed percentage of "cash back" equivalent. So if you're paying for all your Southwest flights yourself already, you presumably know how far the 50000 points from a Southwest Visa will take you (because you presumably already have a strategy for when to use Southwest points vs when to pay, even though the price of both goes up and down together).

United / Star Alliance redemption is by zones, so that's non-linear always. That means that if you can find "saver" redemtpions where the money ticket cost would be high, you get a much higher rate of return.

So with UA miles, you can pay for the flights which are cheap and redemptions are costly, and can redeem miles for the flights which are expensive and redemptions are cheap. With Southwest points, you don't get that "leverage"; it's just that one card signup with some spend can get you some number of free flights once.

So is your goal to save a couple percent "cash back" equivalent, or is your goal to save on the most expensive flights? If the latter, then it would seem to make sense to collect more UA miles in more ways than worrying about collecting Southwest points (especially since Southwest uses the same bank, Chase).

Btw, where do you stay after you get off the plane? Are you mostly visiting friends/family and staying with them, or mostly paying to stay somewhere? If you airline mile collection makes most sense on UA (and thus Chase), you may think about whether it's hotel points you should diversify to, and in that case pick hotels that have cards with banks other than Chase, so that you can concentrate your Chase applicaitons on getting more UA miles and balance that with applications to other banks to get hotel points.