The frustrating part of the "they should focus on older characters" argument is it often invalidates the victories newer characters have.
Like Pyra/Mythra were a few years old when they were included. Yet they still are derided in this thread as shill picks. They had already proven themselves to be Xenoblade royalty then and are still incredibly popular in the Xenoblade community. When has a character proven themselves? When does a character just become a popular and important character worth including and not some "blatant advertising?"
Lyn was brought up as a character who has proved herself, and ya know what, I agree. But I'd argue every Fire Emblem character in the roster except Corrin has. The rest are uber popular and are from super important and well beloved games. Sure Three Houses was new when Byleth was included but it has already proven to be one of the cornerstones of the franchise. Games and characters can and do prove their worth super quickly. There is nothing wrong with celebrating the current superstars. That's part of how they become older superstars. When King K. Rool was introduced, audiences didn't just sit there and say "oh this villain is cool, but I want to see if he has staying power." They went "I like this character and I want to see more of him." Then the character appears more and people are happy. Putting newer characters in Smash is just one way of doing that. Roy and Ike are pretty much considered the old guard now, but they were included when they were very young. Same with characters like Lucas, Lucario, Inkling and... oh yeah.... Pikachu. He was effectively brand new when included.
You might argue Smash should be different but like... why? If you argue Smash is like a museum of sorts, then modern gaming history is equally as important as early gaming history. Even if I think they're (a little) overrated, I'm not gonna pretend Persona 5 isn't still affecting JRPGs or that Breath of the Wild isn't still affecting open worlds. If you argue that more popular characters should get in, then I'd say that the newer characters are still objectively popular (even Corrin who I kinda **** on earlier). If you argue that it feels corporate... well yeah. Making games is a business. Choosing Banjo and choosing Incineroar were both calculated decisions to make money. One route isn't inherently better than the other. Just because a product appeals directly to you doesn't make it better.
Why aren't you guys celebrating Chrom? He's the kind of inclusion you want, right? He maintained his popularity for 6 years until he got in. Is he somehow not old enough even though he join Smash a generation after his debut? Chrom should be a shining example that characters like Lyn are possible.
I want a lot of older characters too, but so often the argument comes off like it can't build up older characters without tearing down the new. Like an old relative complaining that foreigners are taking are jobs. Older characters should be able to stand up on their old merits. Its how "forgotten" characters like Banjo, K.Rool, Dark Samus, and Chrom got included. Their fanbases weren't demeaning newer picks (barring bad eggs). They were surviving off of passion and selling their characters. Older characters aren't being dismissed or insulted when new characters are included.
And I know this isn't going to change anything. This debate has been done so many times its reaching futility. Nothing new is being added to the conversation. It seems you're either opposed go this sort of thing or not with very little wiggle room. I really don't want to discuss this kind of thing anymore because it keeps running in circles. Let's talk about more productive (or at least funny) things.