That’s quite possible, Mat. I agree that most of the contexts for this seem to be in relation to Right Effort.
But ātāpin was used in MN 31 to describe the quality of these 3 arahants -
Good, good, Anuruddha. I hope that you all abide diligent, ardent, and resolute.”
“Surely, venerable sir, we abide diligent, ardent, and resolute.”
“But, Anuruddha, how do you abide thus?”
“Venerable sir, as to that, whichever of us returns first from the village with almsfood prepares the seats, sets out the water for drinking and for washing, and puts the refuse bucket in its place. Whichever of us returns last eats any food left over, if he wishes; otherwise he throws it away where there is no greenery or drops it into water where there is no life. He puts away the seats and the water for drinking and for washing. He puts away the refuse bucket after washing it and he sweeps out the refectory. Whoever notices that the pots of water for drinking, washing, or the latrine are low or empty takes care of them. If they are too heavy for him, he calls someone else by a signal of the hand and they move it by joining hands, but because of this we do not break out into speech. But every five days we sit together all night discussing the Dhamma. That is how we abide diligent, ardent, and resolute.
Right Effort does not appear to have a place here, would you agree?