They say time is money...
Obviously, nobody will spent every minute farming crowns, so let's assume the standard is a "bot" that starts off as a recruit and wants to maximize the amount of crowns earned every minute by playing SK like a normal person (must progress through missions to advance, etc.). After some time, the bot should fall into some sort of pattern that produces the maximum rate of crown intake.
What is that rate in terms of crowns per minute?
Now assume 8k crowns can net you 100 energy. How much USD* worth of time have you deposited into this game?
*I'm f2p so I don't know what's the conversion rate between energy and U.S dollars.
A thread was made to this effect awhile back. A few math geeks went and ran the numbers in-depth and all that... I'll tell you that the pay is lousy though.
Back when they ran the numbers, the best amount someone was getting paid farming the most profitable level as a veteran that logged in every time was around $2.25/hr USD and that's kicking the living carp out of everything in their wake and not getting stuck in any buggy/miscalculated situations.
They turned and recalculated to err on the side of caution and essentially said that $2/hr was the absolute best you would make off the game. That was when energy was fluxing between 6-8k not just 8k flat.
Optimally grinding the money is difficult. But I know some vendors probably eek out a decent $4/hr when they have a good rng day/ an event comes out that everybody likes. But they've probably invested a good $500 worth of energy into the game by that point (be it with a card or their own keylogging).
Games typically will not lend themselves to letting the players get paid unless they have massive playerbase and the player is someone who metagames and meta-markets in their sleep. That guy who made 10k playing Diablo 3 was practically shut-in for the vast majority of his time making that money.
If someone tells you they make money playing videogames.... videogames are their job. Simply put, once you get to the point you're making a wage off a game, you're probably not enjoying it half as much anymore.