It seems like you've already outlined most of the reasons why this is the way it is.
The game has a history of making things long and tedious and annoying. Zeta weapon? Anima weapon?
237 FATES is not very much. FATES spawn relatively fast and, in a group, can be completed in a minute or less, especially FATES with a single boss. I'm sure in 1 hour you can complete 30+ FATES in some areas.
If you did FATES for just 1 hour every day in a group, you could complete 900 in a month.
Just 1 hour a day in a group. It's fairly reasonable for most casual players who want every weapon.
Many people will do it for much more than 1 hour a day.
We have to think about what is reasonable compared to the request.
If the request is to get every single weapon and the special mount, then doing FATES 1 hour every day in a group over 2 months sounds very reasonable to me. The effort must match the reward.
You said "stretched over the span of a bit over two months, by the end of it hopefully most people who want to get it will have it." So, if it is attainable after 2 months, why should it be changed?
Why do we need instant gratification instead of making a concerted effort over time?
This isn't the type of event that people are supposed to "just get done". It takes time. It takes effort.
But this event is not just about "playing the regular game". It's a special event that requires extra time and effort.
There is no reason to give instant gratification to every casual player.
Then the event loses meaning.
I don't know about in other servers, but in ours there may be 20+ groups in Party Finder at any time recruiting people to run through FATES as groups. I see them in zones and they just plow through FATES with lightning speed.
I think one of the purposes of the event is to work together to get the weapons. I don't think every single weapon and the "special mount" is meant to be attainable by every player.
I'm not trying to make the reply sound rude. I am sorry if it sounds that way. Just trying to rationalize why the event is the way it is and why it probably won't be changed.
It just seems to me like many posts are about "This is not convenient for me. Here is why. Please change it."
But many people are doing the event without any trouble.