@76Texan - I couldnt resist myself LOL .. its really THIS simple:
Kubiak inherited a "nucleus" of - his only pro bowler was the fastest man in the NFL Jerome Mathis woo hoo!! It was a special teamer HAHA .. however for grins and giggles I went down each roster and for Koobs the most notable players I could find were David Carr (#1 pick), Andre Johnson (future All Pro), Jabar Gafney (of Patriots fame LOL) Steve "not so skinny" McKinney (above average I guess), Seth Payne?, Chester Pitts (above average), Dunta Robinson (pro bowl level), Gary Walker (first Texan pro bowler, but past his prime), Kailee Wong?? thats it - that was what Kubiak inherited. LOL. Best QB Kubiak ever had was Matt Schaub and until he imploded was always a top ten stats QB in the league under Kubiak. Koobs never had a blue chipper here.
Obrien?
Duane Brown and JJ Watt were All Pros, Andre Johnson was in the twilight of a possible HOF career (and subsequently eradicated by OBrien), his roster included guys like AJ Bouye (future All Pro), Brian Cushing (pro bowler), Owen Daniels (pro bowler), DeAndre Hopkins (future All Pro), Kareem Jackson (pro bowler) JJO (pro bowler), Shane Lechler (HOF?), Ben Johnson, Wade Smith, Antonio Smith (all above average?), Earl Mitchell, Arian Foster was on that roster and gave OBrien 1200 yards the next year. Bill Obrien never developed a QB. It wasnt until Deshaun Watson was "forced upon him" that he finally was able to look competent in the passing game, and in the victory column.
Pretty obvious example of REBUILD vs RETOOL.
Now that we had settled on Kubiak's rebuilding vs. OB's retooling, we can move on to how the Texans had fared on the playing field during the first 5 years of each HC's tenure.
(I could include the 6th year, but that would give OB the advantage of having guys like Tunsil and Stills - whom OB had used future draft picks on.)
Here are the AFC South's non-conference records, besides the Texans':
2006: Colts 9-1, Jags 6-4, Titans 4-6, Total 19-11
2007: Colts 8-2, Jags 9-1, Titans 6-4, Total 23-7
2008: Colts 8-2, Jags 3-7, Titans 9-1, Total 20-10
2009: Colts 8-2, Jags 4-6, Titans 6-4, Total 18-12
2010: Colts 6-4, Jags 5-5, Titans 4-6, Total 15-15
Combined records: 95-55
......
Guess what those numbers were under OB?
2014: Colts 5-5, Jags 2-8, Titans 1-9, Total 8-22
2015: Colts 4-6, Jags 3-7, Titans 2-8, Total 9-21
2016: Colts 5-5, Jags 1-9, Titans 7-3, Total 13-17
2017: Colts 2-8, Jags 6-4, Titans 4-6, Total 12-18
2018: Colts 6-4, Jags 4-6, Titans 6-4, Total 16-14
Combined records: 58-92
....
Under Kubiak, the Texans played against much better opponents.
O'Brien was just in a lucky situation.