Regarding seeing 13.1 earlier, I don't think so. Let's assume for the sake of argument that the team at Apple decided about 15 July that they were going to accelerate phone production to avoid any potential tariffs. At that point, we were at beta 4, I believe. But Apple internally was much further along. They gave themselves a cutoff date of, say, August 20 to have a "13.0" ready for the phones being produced but with a feature freeze. If your feature wasn't going to be ready for that cutoff (think Automation), it got the ax from 13.0 but got moved to 13.1. But they also wanted to keep pushing development of the overall 13 tree. so they kept moving forward on that separate path.
Again, you are making the assumption that 13.1 is a true "dot 1" update and not just a naming convention to denote development of 13.0 past the new phone software flash date (which is my operating assumption). The past informs the future, but if anything, Apple has taught us that it doesn't constrain the future. They have changed so many things about how they deliver these betas over the past 2 years that there is no way you can use their past practices to predict what they will do in this regard in the future.
So, the new phones are due to be released on September 20th, Apple start bundling the internal GM release onto those devices starting a month beforehand. So your cutoff date is actually the usual cutoff date, which is why Beta 8 was last beta and will be the GM.
If you're right about the tariffs, then they would have done it MUCH earlier.
The 2 features re-introduced, are not significant enough to warrant a rush release of 13.1 for the day of the phone release. So go on, tell my why those features are so significant enough that they've rushed a 13.1 release, rather than leave it til later, and done a 13.0.1 day 1 please if there were any bugs missed due to rushed shipping for tariffs?? A x.1 release tends to be over a month after a x.0 release, but it could be that due to rumoured new Watches, or something they will announce at the event, but not released the same day as the new phones, that they're wanting that x.1 release earlier than normal, possibly the end of September, or early October. This is much more likely than your Tariffs goes.
Also, you keep missing out the point that it makes no real sense that they would rush a x.1 beta to release in a less than 4 week period for Developers to test their apps, as some are massively broken in 13.1 b1 and already seeing them not being resolved in b2. Adobe Creative Cloud & Fitbit still seem broken and that's a big one to have broken still.