This isn't a bug as much as just an opinion.

I'm not sure what others think, but in my opinion the new "grass_block_top" texture looks too flat.
The old one was much better.

Older:

New:

As you can see the new one lacks the dimension it had before, and looks so flat.

As much as I agree with you that the new texture is worse, this isn't what GitHub issues are meant for. All Faithful textures go through a period of community voting before being added, and so did this one. Subjective matters and other non-bugs like this should be discussed in the Faithful Discord server.