I mostly agree with you. I don't know how the specs compare from this new Samsung Tab S3 to the Zenpad 3s10. Does the Tab have a faster chip? SD 820 for the Tab versus a Mediatek MT8176. I'm guessing the SD is more powerful and therefore worth some money. The Zenpad has 64GB of memory compared to 32 on the Tab S, so advantage there goes to Asus. I didn't see any screen resolution numbers in this article so can't comment on that item. Battery on the Tab is only 100 mAh larger than the Zenpad (which has quick charge 3) so that's a wash.
I guess maybe the defining feature to set the Tab apart would be the pen with the baked-in software. If you are a person that will use the pen in a variety of apps then you may just have to suck it up and get the Tab, even though no rational person would say that pen functionality is worth another $300. Any after-market pen you could buy for the Asus presumably wouldn't work as well, but who knows. During the few weeks I owned a Note 7 I tried using it to take notes at a meeting, using OneNote, and the damn app crashed on me 3-5 times during an hour meeting where I would lose 1-2 sentences of handwritten notes.
So yeah, value proposition doesn't seem to exist to justify this price. I will say that I own a Zenpad 3s10 (purchased Dec 2016) and have been very pleased with it. It is fast, almost never lags on even memory-hog games, and has a very nice screen and speakers. The only issue that people (including me) seem to be having is random issues with the power just cutting off when you try turning it on from the "off" state. This requires a hard reset (power + volume up/down) to fix. I think this only started happening after an OS update so I think it is a software issue that will likely be fixed via OTA. Otherwise I am 99% thrilled with this $300 tablet. And if I really wanted to start using it for productivity I would get a bluetooth keyboard case and the optional pen and I would be in great shape thanks to all of the excellent MS Office apps.