Glazing is an issue with augured holes in heavy clay. Definitely you want to scar the edges of the hole after augering if you have heavy clay.
But starting with an auger is still a win. After you have the hole, you can attack the sides iwth your tool of choice. (Scraping with the claw end of a crowbar works well.)
I ended up with a contract once where I was digging holes by hand. After 2 hours for one hole, I gave it up and hired a bobcat and auger to do the rest.
I've seen guys who welded a few teeth to the flutes of the auger to make a corregated side to the hole. Since the teeth don't go over and over a spot, the tooth scars aren't glazed. They also give some purchase for knocking glazed bits off.
Here, clay often IS the subsoil. There is no 'punch thorugh the clay to the gravel' it's solid clay down to bedrock.
One of the things I do when recommending trees for people is to ask them to do a percolation test. Dig a hole two shovels (16") deep. Fill with water, wait an hour, refill with water. Measure the water level after another 2 hours. If there is more than 8" of water in the hole, they have very heavy soil, and their choice of trees is restricted, or they have to put the trees on a mound.
Most of the time, clay soils aren't as heavy as you think. Watch for the color shifts (blue grey, green-gray) that indicate a majority of time spent in anerobic conditions. Sniff for rotten eggs, which tells you that the organic matter is decomposing in anerobic conditions. These say, "don't plant the wrong tree here."
My own farm is wildly variable. We had glaciers here a few thousand years ago. I have zones of nearly pure sand, to silty sand, to sandy clay to pure clay to pure peatmoss on top of clay. Sometimes holes augered 15 feet apart will show entirely different looking spoil piles.