Merch is a very poor meter to see who would join. We had it work only once, with the Jinbe coin, and never before or again. Plus, it only worked on the Jinbe coin because the coins for the Straw Hats were gold-colored, and Jinbe was the only non-SH that got a golden coin. It clearly put Jinbe in the same level as the Straw Hats. Sometimes, I think it was a gambit of the company, much like the Yamato towel probably was, and not the result of insider knowledge.
Popular characters seel merch. Merch companies will do anything to boots sales. Shueisha and Toei will too. Yamato's debut in the anime came with a ton of merch, enough to make anyone think Yamato was sure going to be a crewmate. Yamato also got an anniversary post in the official Instagram, something only Straw Hats had gotten so far. But it came right during the full season of Yamato hype.
So, don't trust merch.