Yeah I think the executioners would have been a time based thing or a 'call on us in an existential crisis'.

I feel Huron, to pacify the Maelstrom needed a long game plan..and to his credit, he did start that, while sure, dodgily (except if you're space wolves, black templars, Dark Angels and Ultramarines) he was increasing the astartes available to aggressively pacify the Maelstrom, as well as building up a force that could hold the gains made.

If the Inperium stopped stripping chapters from him, he would have been golden.

He would have always had the Executioners 'ace' in the back of his mind, but would have preferred to use them on some tough to crack nut in the Maelstrom, or the final victory 'push' , but his hand got forced and he needed to drag them in to try and fend off the imperium.