You guys are both right and wrong.
Here's the timeline of Letoker.
Leto is announced as the new joker and people were happy.
First photo of Leto as joker gets a mixed reaction because of the teeth and tattoos, especially the "damaged" tattoo.
First set photos get people optimistic.
First teaser from SDCC gets everyone excited for Joker and the film because it looked like he was the main villain.
The media starts reporting that he's taking things a bit too seriously on the set and people are a bit turned off.
Second trailer was cool, people still looking forward to Letoker and company.
More stories about on set antics emerge and Leto starts to look like a ****** bag, but whatever.
The reviews and first reactions for the film aren't positive.
Leto does interviews talking about how deep he went into the role and how it was "painful."
People start losing hope, and the ongoing stories about Leto's method acting begins to make people dislike Leto
The film comes out and Joker was barely in the film and his role and acting in it doesn't in any way justify his on set antics and people turn on Leto because he looks like a hack after all the method acting talk.
Finally, Letoker shows up in a rap video that sucks too.
As far as the merchandise sales, I think most of it sold well. The purple coat Joker didn't, since it's available below retail price, but all others sold out... eventually. As for other companies, they also sold pretty well.
I think it sold well because most of the figures were actually good looking collectibles and the design of Letoker, while not great (imo), it was unique enough for people to like even if they didn't like the movie or character.
Even I almost bought the HT tuxedo Letoker because the figure looked so good and film accurate. Difabio convinced me not to get it and I saved $200+ dollars.