I found a way to make this level comfortably marathon safe. Adding in hoplites inside walled sections make quick work of trapped horse archers. They also have the upper hand vs priests. Finally, they are good at taking out buildings as well. Given great unit placement and conversion RNG, and minor optimizations, I think hoplite strats could even be used for new IL WR run here, but I'll maybe try it later. I was quite sloppy here as I completely forgot to put priests next to the catapults in the middle.

I tried this strategy 5 times. It worked every time; this was the fastest attempt. I believe it is very marathon safe. Full info in video description.