For a non-P6 team, that is absolutely a successful season. You can finish in the lower half of the B10 and still make the tournament. That isn't a successful season IMO. For a P6 team, I'd say a 7 seed or better is a successful season. I suspect that getting a 7 seed on 20 wins is rough.
Testing my hypothesis -- all Seeds 1-7 w/20 or fewer wins:
2022: AL(6), tOSU(7) each w/19 wins
2021: Shortened Season (Many teams with 20-25 games total)
2020: Cancelled
2019: ASU(5), UCLA(6), each w/20 wins
2018: FLA(6), TXA&M(7), each w/20 wins
2017: None
2016: TX(6), WI(7), OR(7), w/20,20,19 wins respectively
So it is tough, not impossible. With the NCAA mostly disregarding Q3/Q4 games now, I suspect it will be more common. Teams can play harder schedules and get invited over the teams padding the win column.