There's money to be made online even at medium stakes, especially if you exploit over GTO play.
That might be. But as others have said, this hand is not a good example of exploitative play. Its a standard cooler both preflop and postflop, and the way, you played it, loses you a lot of value in the long run. So you are "exploiting" yourself with this kind of line, not the opponent. If you 4-bet preflop, AK is not going to fold. He is either going to call in position or 5-bet. In which case you can get it all-in as a 70% favourite. So slowplaying did not win you anything extra against his actual holding. And most of the time he miss the flop and dont put in a lot of chips postflop. Maybe you get a C-bet out of him, but then thats it. Or flop comes AXY, where XY is not a K, and then he has outdrawn you.
And postflop check-jamming the flop more than 100BB deep is simply bad. You are forcing him to always have a very good hand, when he gives you action. Like at least two pair, as in fact he had. And if you check-call or check-raise small, you are going to stack those hands anyway. Whereas if he had a hand like AQ, AJ or some kind of draw, then he is most likely just going to fold those hands facing a massive overbet shove on the flop. And its not even like, you had much to protect against. You had K of hearts, which makes it far less likely, he can have a flushdraw. And if another heart comes on the turn, you will have a redraw to the nut flush as well as a boat. This line almost looks like, you are scared of seeing a turn and river, and this is definitely something, you need to work on.