i'm just gonna go ahead and put this out there for anyone also hating having the "for you" tab firston desktop--i figured out a way around it.
first step: go here and download the redirector extension to your web browser of choice
after that's installed, click on the extension and select 'edit redirects'. you're going to add a new one here. you'll create the two redirects in the picture below, which i'll describe as well.
so for the title, just something like "automatically redirect to the following dash" is a simple enough description.
i entered the same url into example and pattern, which is https://www.tumblr.com/dashboard/stuff_for_you
you want the redirect url to be https://www.tumblr.com/dashboard/following
i picked regular expression since i'm just using the literal urls and i don't want other things on tumblr to redirect to here
then i clicked "show advanced options" and checked all the boxes--now i'll be the first to say that i don't know everything about this, so i went a bit overboard, but it does work so that if you click the home button on the dash or land on the page from another link, you'll always be redirected to your "following" tab
duplicate the redirect you just made and go to edit it
change the example and pattern url to https://www.tumblr.com/dashboard
keep everything else the same
this should redirect both a general page refresh, clicking the home button, and logging in to the "following" tab by default. i can't say that this fix will last forever, or that it's perfect--it is a redirect afterall, so it could cause a lot of loading/slowdown if your network connection is bad--but it's as close as i've gotten to putting the following tab first and getting one's dash back to what it was prior to the forced change to "for you" first.
edit: if you don't use infinite scroll and have tumblr load as pages, you'll want to add something to that second tumblr redirect in order to get to see posts past the first page. under the advanced settings option, put https://www.tumblr.com/dashboard/following? in the exclude pattern area. pages should work after that.