You do realize players like Xeno clear Ultimate long before any of these programs even work, yes? His viewership spikes on new content release because it's new and players enjoy watching him. Third party plugins and the like won't impact this whatsoever because the whole point of Week 1 or WF racing is how quickly they clear not simply showcasing the content itself. Most people watching his stream either can't raid themselves, have no desire to or already have statics that simply aren't running 12+ hour days. Hence why they watch, instead. Plugins have nothing to do with it.
Which isn't all that surprising. A lot of people don't want to invest the sheer amount of time blind prog demands. Or they simply don't find it fun. To each their own and all that.
You should really take your own advice. First and foremost, only two streamers were banned. Neither one of them were cheating. They used a UI plugin which put abilities timers on the party list, something Yoshida has even said they're considering doing themselves. If you're seriously going to call putting a timer under Nascent Flash on the party list some massive gameplay cheat, well, you may want to scroll up and see what actual cheating looks like. Nevertheless, both were banned entirely due to report bombing. We know this because 5chan literally orchestrated it to "see whether SE was serious." In the case of the more recent example, practically everyone has denounced that as cheating. There's a massive difference between the JP streamers adding buff timers to their party list and someone who had a mini-map which displayed how to execute every single mechanic.
This is some tinfoil hat nonsense right here. The devs have never added "traps" or done anything of the sort. If they did, maybe they'd actually catch the multitude of bots destroying the crafting aspect of the game. Nevertheless, that isn't how developers work because it wouldn't be efficient. You're assuming these third party programs wouldn't be able to detect changes to the the very code they hook into to operate. Even on the assumption they couldn't, which is a massive assumption, it takes just a single person being banned for the programmers to immediately work on an update to get around it.
Nonetheless, it's not arrogance but simple pragmatism. Banning third party programs like mods, ACT and the like isn't cost efficient for SE. They will lose a sizable amount of money while gaining absolutely nothing for it. Hence why a certain website has been around for nearly a decade now.