The problem with ordering online is that only about 80 percent of the stuff makes it to your door unscathed, based on Terry's experience. That's why, if you do order online, you need to order from a vendor with an excellent return policy and excellent customer service. I know a couple that have that reputation and the company you mentioned isn't one that I, at least, am aware has that reputation. I would let them know that the tank was damaged in shipment and you want a replacement. Period. Or you are stopping payment on your credit card. Nobody should be unfriendly to a customer who calls with a complaint that they can reliably expect to hear on one out of 5 orders.
The semicircle is for the wires to install the auto-flush mechanism on a newer Toto washlet. All the newer Toto tanks have it.
That vertical line, however, does seem strange to me. It does look like a repair of a casting defect. It looks more like something I would expect to see from AS than from Toto, so you may have a point, given Toto's stellar quality reputation. That, I might call Toto about. The damaged-in-shipping issue likely isn't Toto's fault.
Your tank also could have cracked from the shock of the cold water being added, which does happen sometimes, albeit less often than it being cracked when shipped by an internet seller.
I will just say that your participation in the forum is welcome. Don't let it get you down when a bunch of other posters tell you what a mistake it was to order online. Four out of five times it works out okay. But with those odds, and the fact that local tradespeople tend to have established relationships with local suppliers who give back to the community by sponsoring the local kids' softball team or whatever, you can understand why there is a strong bias on this forum towards buying local. (And in most cases, you can get a decent price on Toto locally, but only if you call around to a lot of places, because many will indeed want a higher markup than others.)
By the way, I suspect that in another year or so, there will be much less of a gap between online and local as far as price goes, as the online merchants may adjust their prices upwards a bit to compensate for the cost of all the damaged porcelain they have to eat, as the carriers either raise shipping rates or disclaim liability for damaged porcelain, and as more local merchants feel the competition and make the Toto product available at a price closer to Terry's fair prices.