There is one way to make $400k/year flying only once a month, but it involves a little more work.
A senior captain showed me how it works, with the contract and various scheduling/trading tools. Basically it's a "cartel" style operation with a very senior guy managing the trades. Trades go up and down the pyramid like a big money laundering scheme. A senior guy bids on open time premium he doesn't want, then gives it away to someone more senior than him (explained to me that this is the only legal trade whenever seniority determined an award). At that point it's laundered, and the senior cartel trip broker now sells that trip down to more junior pilots for a small commission, keeping only the trips he personally wants for currency.
Also, trips can get split up which adds TFP for deadheads, picked up premium, then recombined by the senior guy which preserves the extra tfp and premium and again, sold back downhill.
Does it really happen? I dunno, it makes a great conspiracy theory.
However I"ve heard FAs talking about the exact same thing plus on 2 separate base boards I saw printed flyers actually advertising the sale of premium trips for $50 or more, so I know that stuff sort of like this actually does occur, at least on a small scale.
So... yea, theoretically a "cartel" member could make a ton of money and not fly much at all, depending on their position in the pyramid. In reality? Nobody actually doing it will admit it to anyone who isn't buying into the scheme, yet everyone seems to know that one guy who is the smartest guy in the room who seems to make a lot of money for not flying much at all, who also has a lot of "friends" he trades with.
Without some sort of trade scheme going on, I also don't see anyone here making $400k flying one trip per month. Spirit has some scheduling contract rules that allow a senior pilot to create a lot of paid conflicts during the month so I could see a really senior spirit pilot *before their new contract* making a ton of money by bidding conflicts and playing various scheduling games, but not here.