I am not an expert at evaluating cheese.
But I have to say, as a DM I really like it, when players find smart and creative ways, to deal with combat, instead of just headbutting into everything. I don't mind if a combat becomes one-sided here. The encounter was still a challenge that was solved with a good plan, instead of just raw stats and luck.
Of course to keep encounters a challenge, the DM has to make sure the same trick doesn't work in every fight. But that is a matter for future encounters.
The Wood Woad's weakness to fire and the twines' flammability made it so tempting to use the Flaming Spheres they were begging to be let out and unleashed. I don't think the Spheres work as well in other situations since Moonbeam is usually better.