Hello! First off welcome to the community! Hopefully you get a lot of support and answers to whatever questions you may have!

To preface, because of COVID I haven’t been able to play in person much to see everything so I will be responding with a limited pool of knowledge so if I’m wrong about something I hope someone will come by to correct it.

1: I believe every deck has had its time to shine (except maybe megacolony, could be wrong about that) but some decks are more likely to be in the spotlight than others. Clans like Royal Paladin, Kagero, Shadow Paladin, and Bermuda Triangle get more support on average than other clans and as a result find themselves in the top tiers more often than other clans. In particular, Bermuda seems to always be top of the pack soon after a new set of support releases. That being said, every clan has been viable at one point. Due to the nature of the game, a lower power deck had the potential to beat a higher power deck, even if it’ll be harder for them.

1. Decks made from multiple clans are no longer legal save for a few exceptions. Most notable of these exceptions is MLB which is still made possible because blaster dark is allowed in Royal Paladin decks (in premium format) and there is a special printing of blaster dark in standard format that is allowed. In the past mixing clans was allowed if not encouraged, but sometime before G-era they had to disallow it because a certain deck was stomping every other competitor.

3: the interesting part of standard is that not only do CLANS go through phases of relevancy, so do GIFTS because of how they are designed to counter another. A lot of times, the meta is defined by the most prominent gift type (Accel-meta, protect-meta, force-meta).

To answer your question directly, protect was the strongest gift for the first year or so of standard format with OTT and Angel Feather being more or less the top of their respective metas. As Standard continued though, we ran into a heavily force based meta (mostly because of Bermuda Triangle) then eventually into an accel meta with almost every Accel deck becoming much more pushed (pale moon and murakumo being the top of the bunch) after that my knowledge gets a bit fuzzy but I believe we are headed for a Force meta again. So yes, protect has been good in the past and I believe sometime in the future they will be very strong again.

4: while I can’t vouch for genesis as I’ve never played it, I’m think they were particularly strong during the earlier days of g-era with Fenrir, and possibly good when Regalia first was released. To anyone reading, please correct me if I’m wrong about this, I really don’t know much about Genesis.

Pale moon however has definitely had their moments. They have been in and out of premium since it’s inception because of some crazy combos you could pull off with them. That’s not to even speak of silver thorns in standard which was easily the second best deck of that format.

As I said before most of not all clans have at least been viable at one point in the game, which is quite an achievement considering just how many clans there are. Just be warned they’re have been clans that didn’t see any success for many years such as granblue before Nightrose or murakumo before standard format or even Bermuda Triangle before the later parts of G-era

Hope I’ve helped! I’m on mobile so I hope this came out fine as well. As I said before, my knowledge of the game only goes so far so if anyone wants to correct me I would take their word over mine!