Vigour varies between clones. Transplanting can give a shock and set the plants back. The plants could simply have been at different stages for development when you planted them.

All good reasons for there being a difference between the plants, of course there are others and providing the conditions are similar they should both do well,(it's not sitting in a permanently wet spot or on top of builders rubble or anything??) I would think you should leave them a year as messing around digging it up will only set it back further if there's nothing wrong....and if there is something wrong...what would you do about it anyway.

Tell the nursery in writing that it's looking poorly but that you taken all reasonable care to plant them both properly, and that you're leaving it in situ as the best course of action, if it later dies you can take it back as having noted now that things were not right.

Cheers Greenmanplants

most hellebore orientalis plants purchased through the nursery trade have been grown from seed as opposed to divisions, which will be true-to-type of the parent plant. Ex-seed Orientalis hybrids are notoriously 'Variable' in terms of plant size, flower size/shape - you name it every variable characteristic is liable to show up! yes, including the first 'doubles' !
I've found that some of the runts of the litter will actually come right by the time they fully mature i.e. 3 or 4 years and I then thank someone I was too busy (read that 'lazy'!) to dig out those runts in their first couple of seasons. My best performing and most spectacular flowering plant was in this category - maturing and improving like a fine red wine in more ways than one.
So agree with greenman, leave it alone for another couple of years - bythat time you'll know for sure, plus your good specimen will be old enough to divide and shift over to its spot if it still not performing.

Thanks!