The Welsh region crashed out of the semi-finals with a 18-11 loss to Munster at Thomond Park on Saturday. But Johnson has hailed his side's fighting spirit.
"We got out skilled and let ourselves down especially at the set-piece," said Johnson.
"I don't think we're too far off Munster. But as I keep saying, when the remits of the game change we need to adapt to them. When you look around I think we're quite similar to Munster.
"Last year we had a real opportunity and finished the season with an amazing run. We haven't been able to do that this time.
"But we showed good courage and commitment to go in at 8-3 at half time. That took a lot of hard work and graft to hang in there.
"Things didn't go our way in the second half but it was great to see that the boys refused to throw in the towel. It's wonderful to be around the character of this group."
The Ospreys will lose a number of high-profile players in the off-season but Johnson is confident in the young players he has blooded this season.
"I'm a glass half-full man," added Johnson.
"It's been frustrating at times. But I have been really pleased with the young guys coming through. Although they lost on Saturday that will be a real good experience for them."
Guinness PRO12
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