Angie, I'm late here -- so sorry. Am mostly off the forum for a few weeks due to work. And I haven't read all the comments. But first -- I am so sorry!! SOOOOO frustrating!!
AND, I also had to laugh, because I could have written a post with the same title this week! Not due to waterproofing issue, but because my favourite Aquatalias (the Gail, in Finds) split a seam for no apparent reason!! They are out for repair as I write. I have no idea what went wrong.
Anyway, back to your boots. First, I would say that slush is really different from rain or dry snow. If you go back a few years to my annual footwear complaint posts, you will see that many people told me, "Just wear your nice booties" in slushy conditions, to which I could only reply, are you insane????? (Pictorial argument below).
I would not wear my knee high Genna Aquatalias in the conditions below. I would not wear my Aquatalia booties in those conditions, either.
I would wear and have worn my dressier/ more refined Aquatalias in heavy rain and/or dry snow. Without any problem.
I also wore my beloved grey Aquatalia booties in the deepest downpour you can imagine, and one bootie did then (forevermore) leak at the toe seam, but honestly, this was a deluge. And my feet were immersed in deep water for about an hour. I couldn't reasonably complain.
The boots/ booties I wear in slushy or truly wintery awful conditions are my La Canadienne Cally short boots, with a lug sole. They keep me warm and dry no matter what. Brilliant boot. They are not even billed as "winter" wear by the company -- only as "autumn" worthy. But they work for me with wool socks. Their true winter boots are even better.
I also wear my knee high La Canadiennes, which are dressier, but to be honest, I wouldn't be out in the absolute worst weather in those for very long.
Of course I also wear my Ugg Adirondack snow boots for more casual/ gearish adventures. Unfortunately, those aggravate my PF so I have to be careful with them I didn't bring them to Vancouver because I didn't anticipate I'd need that degree of warmth or weather proofing -- and even with our colder than usual winter, I didn't.
I used to also wear my Aquatalia Sweetie motos and again, they handled it, although they did wear out faster than some forum members.'
The key is a lug sole or a substantial rubber sole or a small heel or a platform that gets you slightly above the worst of it.
Anyway...my point is...it might not be the brand...but the STYLE. You need to read the fine print carefully and also be realistic. Boots have seams and zippers -- so no matter what, water gets in if it is deep and if you spend a lot of time in it -- unless the sole is substantial enough to raise you above the worst wet. Dry snow is easy peasy to deal with. Rain is fairly easy unless you are walking in deep puddles. Ice and slush are the worst -- ice due to danger, slush due to feet getting wet.
A refined boot is generally not going to work in such conditions if you are out for any length of time. Fine for going from car to destination but not fine for a 2 mile walk.
Phew. That was longer than it needed to be. But you get it, I'm sure! I'm so sorry for the blisters and disappointment.