I picked up a hornbeam like this a few weeks ago maybe worse, because all the leaves were crispy and it wasnt being watered at the nursery. the roots are probably the most compacted ive ever seen on a hornbeam. I emptied a whole 5 litre water can on the pot, then lifted it out the pot and the middle of the root ball was still bone dry! Ive never had to dunk a tree before but i filled a bucket with water and submerged the entire root ball in it for 30mins, and pulled it out when all the air bubbles were gone, then dunked it again. removed a little soil from the top surface just to see what the nebari was like, nothing major. Then just slipped the whole thing in a wider plastic pot and filled in the edges with bonsai soil. its lost all the crispy leaves it came with and is now pushing out new growth. its being watered and fed heavily. want to see it?
newbies are getting it wrong with these nursery trees, instead of wanting to do drastic root work right away, just use those established roots to power growth, you have a whole tub of healthy root there. in the growing season, if you say wanted to do a trunk chop, you have all that root to power back budding and rampant growth. if you wanted to cut all the branches back, it should back bud like mad with all that root power. as long as you water and water runs freely through the drainage holes within seconds its fine.