Possibly easy way to get hero merit?

[kcirrot]

3 hours ago, Hero_Lucina said:

I still have troubles with level 40's. 

OK, but again the Normal difficulty chapter 1&2 Chain Challenge features level thirty-five (35) enemies who do not use their normal skill set.

Thus a group of decently played level 40s should have no trouble grinding there.  It is objectively cheaper and easier than the method you offered in your original post.  You suggest that people use the tenth stratum which features level 40 heroes using their full skill set.