First off, they are 1-4 pre-tebow...not 1-5.
Second, what are you looking for on defensive stats? Points? That doesn't tell you the whole picture because of turnovers. A shitty offense can put the defense in shitty situations.
L Oakland total Yards given up 289 Points GU 23 Denver 3 TO's QB responsible for 2
W Cincinnati Yards GU 382 Points GU 22 Denver TO's 2 QB responsible for 1
L Tennessee Yards GU 333 Points 17 TO's 2 QB responsible for 2
L Green Bay Yards GU 507 Points 49 TO's 4 QB responsible for 3
L San Diego Yards GU 418 Points GU 29 TO's 1...this is when Tebow came in. Orton threw 1 pick, Tebow-0
W Miami Yards GU 267 Points GU 15 TO's 1 QB responsible for 0
L Detroit YGU 376 Points GU 45 TO's 3 QB responsible for 2
W Oakland YGU 416 Points GU 24 TO's 0
W Kansas City YGU 258 Points 10 TO's 0
W NY Jets YGU 318 PGU 13 TO's 1 QB responsible for 0
W San Diego YGU 344 PGU 13 TO's 0
This goes to show the "defense doesn't play better just because Tebow is in the game". Denver has played Oakland and San Diego twice. Once with Tebow, once without. The main difference I see is TO's. It's not like the defense is playing lights out just because Tebow is there. I would say the defense is giving up less points because the offense is not giving the other team a short field. The only loss that Tebow has directly reflects that he was poor at the thing he is the best at...protecting the ball. Denver had 3 TO's in that game, but all other games they average less than 1. Prior to Tebow starting...the Broncos averaged around 3. That is a huge difference...