I've finished the tier as MCH and I can safely say that it simply is not doing anywhere near enough damage right now.

The Wildfire buff mentioned in the OP is a good start but it will probably take more than that to fix things.

The reality is MCH is currently doing about 10% less dps than Reaper -- now while it can be argued there can be some difference there 10% is just way way too much.

I would say the safest way to buff MCH is significantly increase the potency of their 123 combo and Wildfire. (Burst DPS is already ok so that probably does not need to be buffed and it may be difficult to manage interactions with other classes if they did that).