I moved from a Tab S3 to the S6 on release day almost 3 years ago. I was taking college classes at night and was using the S3 to take notes. I upgraded to the S6 to get more storage and faster recognition... I'd buy an identical tablet today -- but maybe not at a $700 price point...
I have the official keyboard case for both the S3 and the S6, and the S3's keyboard case became REALLY finicky during use (disconnecting itself while typing, and being really unforgiving about tablet/keyboard placement). It became unusable, in fact. The S6's keyboard case is orders of magnitude better, thought it has its moments (pogo pins after 2+ years oxidize a bit...). And I think the trackpad is kind of a waste.
At the time, Samsung Notes didn't do handwriting-to-text, and STILL won't install on a non-Samsung Windows tablet. So I wound up buying and installing Myscript Nebo on both my S6 and my Windows laptop. I still use Nebo, even after graduating (though not as often) any time I need to take notes that I may need to send to someone else or when I need to do some brainstorming, since writing just works better for me than typing when I need to just think. Not a bad app for $5. (Now that it's $12, it's still not a bad deal, IMO, but read the <4* reviews before you drop your $, since some of them bring up valid weaknesses that may be a showstopper for you.)
Dex mode? It's OK. I use it 1-2x a month or so, but when you need it, you may REALLY need it if you're trying to get work done on the tablet. Just having a notetaking app, a browser, and Outlook up on the same screen is sometimes really useful. And split-screen just doesn't cut it.