For example, each item currently requires a separate facility, and each planet's specialties and ultimately promethium are required. However, I don't know the benefits of all of this compared to doing quality work according to the existing method.

Existing methods do not require additional facilities for each item, nor do they require the specialties of each planet or the transportation of additional ingredients. They just need more existing ingredients. However, to use this mod, it is extremely expensive and labor-intensive, such as requiring very large additional facilities for each item and the transportation of specialties individually by spacecraft. This makes it extremely difficult to use the mod.

Personally, I think it should be more reasonable, changed, or very easy compared to the existing method.

My goal with this mod is not to make quality easier, but rather to introduce new and challenging production chains similar to other content mods to make quality more interesting than recycling loops.

However, if the costs/balancing are not to your liking, there are many options to tweak the complexity of this mod. I also explained them in more detail in another discussion: https://mods.factorio.com/mod/quality-processing/discussion/68d18d6091babbb95dbc7e97

Thank you for your response. In that case, could you please add an option to remove the Promethium asteroid requirement for crafting legendary quality items?

I added the option, check the mod settings for "No promethium".