Boro's form collapsed in 2013, after they were just about the best side in the Championship before Christmas, and Mowbray said even a long injury-list could not be the sole excuse for their season falling apart.
Steve Howard and Leroy Lita were on target for Wednesday, with three points confirming their safety, and the whole experience left Mowbray feeling flat ahead of a summer in which he feels he needs to strengthen his squad.
"They played how we expected them to play - they didn't have to work too hard for the first goal, it was self-inflicted," Mowbray said.
"The second one, another set-play we conceded.
"(The season was) Disappointing for us: we could have gone top on New Year's Day if we'd beaten Derby.
"So for 27 games we were as good as anybody in this league, for the rest we have struggled, we've won three of them so it should be no surprise to us we didn't get a victory today, we have to get stronger I think.
"Ultimately the squad has to be stronger and deeper and try and sustain it. And hopefully you keep your best 11, 12, 13 players fit for most of the season but we've fallen away, we can't hide that fact, it is what it is."