"For me to sit here and say the Lions would have probably won is wrong. But personally my opinion is that if Eddie Jones went as coach they would have won 3-0. He is that good."
Since Jones took over as England coach the side have lost just one of their 20 tests. They haven't however faced the All Blacks - a team they have beaten just once in their last 15 tests.
"I don't know how he would have done it, but Eddie would have found a way. Eddie has changed our mindset at England from always accepting we can't always be too outspoken and confident and he's really helped us a team to kick on."
O'Brien started in all three tests of the drawn series which ended with a controversial 15-15 draw at Eden Park.
The 30-year-old, who has played 49 tests for Ireland and five for the Lions, said Gatland and the Lions coaching staff mis-managed the training schedule during the five week tour.
"To be honest, I'd be pretty critical of it because I think we should have won the tour and we probably should have won it comfortably," O'Brien said in an interview with Irish radio station Newstalk.
"There's the best players in the world on a Lions tour. I know you are playing the best team in the world but with the quality and strength in depth we had, we probably should have won the tour. It wasn't down to fatigue. It was probably management a bit, in terms of how our weeks went.
"The first week, we definitely over-trained on the Thursday and maybe the coaches were panicking a little bit about getting the information into us. On the first week [of the first Test], we had a triple [session] day, [the] lads' legs were heavy on the Thursday and we were playing the All Blacks on Saturday.
The Lions lost the opening test 30-15 at Eden Park before bouncing back to take the second test 24-21, handing the All Blacks their first home loss since 2009.
A victory in the third and final test would have secured the Lions their first series win in New Zealand since 1971. O'Brien says the squad were again overtrained on the eve of the final game.
"We did nearly a similar thing in the last week. So maybe it's more [from] a coaching point of view, in terms of taking lessons. Less is more sometimes on a tour like that, rather than trying to pick things up at the end of the week.
"There was probably no need for that but it's just the way it was managed. We had said it, at the time, and they pulled back a bit. But it's just about getting that fine balance between players and coaches and making sure the group is ready to rock."
O'Brien was forced from the field at halftime of the third test draw after coming off second best from a Jerome Kaino clear-out. O'Brien revealed to Irish site Sports Joe that after the test he found Kaino and said 'you got me good'.
