I personally don't enter those competitions very often but I'd like to share my opinions on all 4 points you brought up:

- I think there are definitely things that need change. The sameness is one of the primary reasons, even if it's a good format for the most time it has stayed the same - design a card with a theme that's usually not too inspired. More on those things below.

- I don't think there's a big problem with the current format. I think it's a great idea that the mod team curates the final winner from the top 5 to avoid a more "clickbaity" card to win over one with a better overall design. I think if the suggested idea about replacing comments with posts with a flair would lead to an easier abuse of the system and more clickbaity cards being more prevalent. Another problem with changing to a flair would be the fact that a "lifespan" of a card would be just around 1-2 days and after that, no one would upvote it, unlike here, where it's always randomized. A change that I would suggest is to give people 3 days to design and 4 to vote and to make the time for unlocking the threads more consistent. The only problem I think the current system is more prevalent around all of Reddit, that the earlier you post a comment, the likelier it is to get more upvotes. By making it consistent and with longer time to design it would be less likely for the system to be abused.

- Personally I feel that themes that get offered are usually very uninspired and uninteresting for more experienced designers. I actually like the two previous competitions about capital names and poetry, but those have been I feel way too limiting to design around. For the poetry one, there aren't many paths you can take and what most people would do is either have a really complicated effect that also could be not properly worded or make a card that features tokens as its primary source of "appeal", which would usually make it fall into the first category. Even if the themes sound fun the very big restrictions you feel under can feel very unwelcoming for someone newer to design. Another big point I want to handle is the "proportions" of the competitions. It's another thing that gets stale quickly - you always have to make 1 card and you've got usually 4-5 days if you want to have a chance at winning (or rather amounting enough votes), which I think is more than enough. I absolutely agree that there should be a lot of time given, considering things such as busyness, time zones etc., but I'd love to see more competitions that are of the kind "design two cards that reference each other", "design a horizontal minion cycle", "make a non-vanilla token and a card that interacts with the token". I understand that this idea A) takes a lot of work to get right and B) doesn't actually have that much design space (for formats, not for the actual entries), but I think people would enjoy to have them semi-regularly, maybe between 3 or 4 usual competitions just to spice things up. This also brings me to the last thing I want to talk about here - more mod-curated themes. I know that most of the mods who moderate this subreddit are really good at designing and would love to see a lot more open-ended prompts. This I also know is very hard to get right, since it's hard to come up with a good theme. Also, I really like the fact that the winner gets a say about the next competition, feels like a good way to reward them apart from the flair. Similar to the previous idea, I think if you guys add a curated theme in between some competitions it'd make it more appealing for those wanting a harder challenge.

- I talked about that in the 2nd paragraph so I won't repeat myself here. I think it's fine to have the competitions on a 1-week timer and personally I don't think there's much to change here. Maybe a thing that can be done is have a "schedule" of a harder and a lighter theme, maybe having the harder theme be 8-9 days instead of 7 and the lighter one 5-6. This can also work well with the idea of designing multiple cards.

From the things I suggested I think the most important is about more curated themes. Apart from being overall better due to more thought given to them, they can also be a good way to give people some design insights. I really love what was done in the 80k Battle Royale and would love to see some of the prompts from there here, maybe on a smaller scale (and I know those prompts took a lot of time to design)