I think this needs a little more thought
I had a similar experience to yours this season. I was skiing for years in boots that had 2 generous fingers in the shell and it significantly impacted my skiing.
This season I dropped down a full size. I now have slightly more that 1 finger in the shell. I think this is a good compromise between a race boot and a comfort boot.
If the shell size is right, I don't think you will have the cramping you describe. But bear in mind that it really, really is true that the liners will pack out a full size. When I first bought my new boots, I couldn't stand up straight because my toes were jammed against the end. It was pretty uncomfortable. After 4 or 5 days of skiing, my toes now have all the room they need. So I concluded that when you leave the shop you have to be thinking, "Man, these boots are uncomfortably tight. I'm not sure these are going to work" (as opposed to, "Good God, these are absolutely killing me.") But again, I think having 1 finger or slightly more should insure the right shell size.
The shop seems to have made a poor choice for you with the Nordica Olympia GTS 6. Nordica's flex system goes from 50 to 130 (same as Atomica), so they had you at the very bottom end of that scale, which seems inconsistent with the steep terrain you want to do. That makes me wonder about the expertise of this shop.
Finally, it's necessary to distinguish between being able to lift your heel up to, say, 1/2" but no more when you try deliberately (which you can do in most any boot that fits right), and having the heel lift of its own accord while you're skiing and putting forward pressure---that you do not want. You also don't want any side-to-side movement in the heel or forefoot.
The Atomic B80 is described as an intermediate recreational boot, but it has a flex index of 80 (on a scale of 50 to 130). However, stiffness also refers to LATERAL stiffness, so make sure this boot has all the support you need for your double blacks.
The B80 has a pretty wide forefoot (104 mm) and narrow heel. Is that your foot shape?
*** My concern about the Atomic B80 is that if you noticed a significant change in fit in the course of a single day, this boot may pack out considerably more and you may find it too large. You will have, I think, much better luck stretching a slightly too small boot than padding a too large boot. If you're between sizes, you're going to need this fitting.
If you have a wide forefoot and narrow heel, I can strongly recommend the Head S9 (or S11 if you want a more aggressive boot), which has a choice of 2 different lasts (100mm and 103 mm) depending on the width of your forefoot. See my review in the gear review forum and also
https://www.head.com/ski/products.php?region=us&tag=freeride&id=677
The Head Dream Thang would also be a good option. The Dream Thang is apparently replacing the S series, so you could get the S9 at a better price right now. I paid $330 but you can find it for less than that. The S9 is the equivalent of the Dream Thang 10. I found that the Head website offered pretty complete information that allowed me to make an educated choice.
A concern I have about women's boots in the recreational category is a liner that is too thick and soft, which I think will pack out more quickly than the thinner liners in the performance category, or compared to men's boots. However, Head is known for its liners that don't pack out as much as other brands.
My advice is that you research this and think it through a little more before skiing with the Atomic B80s again. List the criteria that you are looking for:
--foot shape
--ability level
--preferred skiing style (speed, aggression))
--preferred terrain
--snow type
And then make sure the boots you try meet your most important criteria. Clarify the return policy with the store before you ski with the Atomic B80s again. Don't be distressed if you have to demo several boots before finding the right one. This is not unusual. Find a shop that will work with you through a few trial pairs.
Finally, be aware that a custom footbed is pretty important.
Here's a good website for ski boot reviews:
https://www.bootfitters.com/07_reviews.htm