If Barkskin raised AC by 2 without concentration until long rest it would be OP to the point of effectively being mandatory when you have a druid in the party. Especially as you could then cast it on every single party member each day.
Raising AC by 2 *with* concentration until long rest is maybe balanced. (essentially an unlimited duration Shield of Faith, at the cost of a 2nd level spell slot.)
Raising AC by 2 *without* concentration for 1 minute is also maybe balanced, but probably less so.
Changing Barkskin to be a 1st level spell makes it too similar to SoF to warrant being its own spell.
