He wasn't that bad with the Texans:
Year 1 - 9-7 from 2-14 the year before
Year 2 - 9-7 won division blasted at home by Chiefs 0-30
Year 3 - 9-7 won division, won wild card round, lost at NE in divisional round 16-34
Year 4 - 4-12 last in AFC South - this was Watson's rookie year
Year 5 - 11-5 won division lost to Colts in wild card 7-21
Year 6 - 10-6 won division, won wild card, blew giant lead to chiefs in divisional lost 51-31
Year 7 - 4-12 - fired half way thru the year
That's not all that bad and had he not blown that 30 point lead to the Chiefs in the divisional round I think the guy is still coaching the Texans. I know the AFC South is bad but the guy won his division 4 of the 7 years he was coaching there and that is going the first 3 years without a QB, go look at the folks they started.
Hubris was his mistake when he made himself GM and traded D-Hop away plus blowing a 30 point lead to the Chiefs is what did him in.