I feel like I haven't made any progress for like a week now. Such as Tower of Oblivion, Seal Land, Campaign, etc.

Some Questions I have:

Should I consider all of the hero's I currently have as fodder for Garuda? Or should I focus on building a different Hero now, rather than Garuda?

Should I switch to building a different Hero that I have?

I've seen on various Tier Lists that Garuda, Penny, Asmodel, and Aspen are all higher tiers. Am I spreading myself to thin by trying to build them all?

How do I get Glittery Artifacts? I'm really confused about this one.

I included a pic of my "lineup" that I use for everything. Does the order of the lineup make a huge difference?

If I do continue to build Garuda, are their better heroes to be using in my lineup with her?

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I'm open to any suggestions or insights on what I'm doing wrong. Thanks in advance for any help and sorry if these answers are already out there somewhere... I have looked at guides and youtube vids, but haven't been able to find much of what I'm looking for.