You may not be wrong, but your position doesn't seem to be clearly supported by the recruiting rankings since A&M went to the SEC. Since 2012, here are the rankings of each school's classes as evaluated by 247:
2012: Texas 2 Texas A&M 16
2013: Texas 17 Texas A&M 9
2014: Texas 17 Texas A&M 5
2015: Texas 10 Texas A&M 11
2016: Texas 7 Texas A&M 18
2017: Texas 25 Texas A&M 13
2018: Texas 3 Texas A&M 17
2019: Texas 3 Texas A&M 4
2020: Texas 8 Texas A&M 6
2021: Texas 15 Texas A&M 8
Looks pretty even to me. Each has had the advantage over the other about half the time, with the years where there was a significant gap also split pretty evenly. So you could say "yes but Texas would have done even better had A&M not taken some recruits away by virtue of their being in the SEC" but that would be pretty hard to prove. Bottom line is Texas and A&M have fought it out pretty evenly in recruiting over the last 10 years, and in my mind at least, both have regularly underperformed on the field relative to their recruiting.