NB and KT have, a few. Capcom has, like, 30!
I wouldn't say that many, especially when the most notable picks for Capcom overshadow the rest, which are a Resident Evil character in general(whether it be Chris, Leon, Jill or Claire), the Monster Hunter, Dante, Chun-Li, Zero and Phoenix Wright. Others, like Amaterasu and Arthur, do get alot of mentions, but don't get picked nearly as often as those six.
Namco, despite not having many, are still very notable and quite up there with those six.
-You have a Tales of character, with the highest pick being Lloyd with Yuri being second, and later with Alphen and Shionne possibly entering the scene with Tales of Arise doing very well
-You have the Chosen Undead from Dark Souls and you have KOS-MOS due to the Monolith Soft connection and her appearance in Xenoblade 2.
-Aside from them, the only other character who tends to get attention is Nightmare from Soulcalibur, but of course, some people didn't really look at him since no one thought of him getting in over Tekken, which is true.
Whereas yeah, Koei Tecmo's most notable character is Ryu Hayabusa. But that's not to say that their Warriors and Dead or Alive series aren't popular. Kasumi gets alot of mention for Dead or Alive, while Lu Bu gets mentioned alot regarding Dynasty Warriors. And I think Japan had quite an interest in Atelier Ryza getting a rep since it was apparently enough for the creators to be asked about a Smash appearance, although whether Atelier Ryza belongs to Gust or Koei Tecmo, I'm not sure.
---
That aside, if you take mergers into question, of course Smash can greatly benefit from all of them.
-Capcom would practically be the coming of Nintendo vs Capcom, Smash Bros. style. Or heck, Marvel vs Capcom featuring guest stars from Nintendo.
-For Namco, not only do you have Tales of, Dark Souls, Xenosaga and Soulcalibur, but now there's also .hack, God Eater, idolmaster, possibly Digimon, Klonoa, Taiko no Tatsujin, Splatterhouse, all of their Arcade classics like Mappy, Dig Dug, Tower of Duraga, Valkyrie, Baraduke, etc and the Namco X Capcom/Project X Zone OC characters(since I think those characters belong to Namco/Monolith). Not to mention franchises for stage ideas like Ace Combat and Ridge Racer.
-Koei Tecmo has Ninja Gaiden, Dead or Alive, the Warriors games, Fatal Frame, Monster Rancher, Nioh, Romance of the Three Kingdoms, possibly Atelier, Toukiden, Deception, and their OC characters from the Nintendo games they've made, like Hyrule Warriors and Age of Calamity.
Sure Nintendo would benefit the most from either Capcom or Namco(especially when taking into account Namco's experience with Smash Bros.), but Koei Tecmo certainly wouldn't be a negative to Smash, especially if it means the Nintendo games that Nintendo didn't include in Smash even as Spirits, like the original Hyrule Warriors, can be referenced without issue.
I thought Activision didn't own Candy Crush.