Sure Haley should get credit, but not for what you have implird. Haley gets credit for runnung interferevpnce for and taking Warner's side in putting together the offense Warner wanted and not what Whisenhunt put together.
IF you can remember, during the Cards offense during Whisenhunt's first training camp and pre-season where he had the QB competition between Warner and Leinart was a 50/50 run/pass standard Steeler type offense that Warner handled and Leinart struggled with. After Leinart melted down in his last pre-season start against the Raiders, Whisenhunt had to declare Warner the starter by default.
After Warner was declared the starter, Warner got Haley to agree to begin changing the offense to suit his talents and particular skills. As the story goes, Whisenhunt did not like that at all, but Haley took Warner's side and got Whisenhunt to agree to try it on in interim basis to see if Warner's offense was better than Whisenhunt's designed offense. There were even several news stories of these big changes along with Haley gushing on how Warner would come in every week with new plays designed to attack this week's opponent' defense. The stories left out any mention of Whisenhunt being in the loop in formulating each week's offensive game plan. These stories are still out there on the Internet and all tell how Haley went to bat for Warner against Whisenhunt's resistence to change the Cards' offense to suit Warner. That is why Haley gets credit for making it possible for Warner to play at the top levels of the NFL again. Check it out, those reports are still out there. Just as Whisenhunt had no success after Warner left, Haley had no success as a head coach for many reasons including he did not have a former NFL MVP to take control of KC offense and attack opponents' defenses.
Joe Montana found greatness in Bill Walsh's West Coast offense, but Montana would never have done well in the Raiders's big pass offense, so that is why is was crucial for Warner to have an offensive system like the one he formulated in St Louis and the one he made here with the help of Todd Haley who ran interference for him with Whisenhunt and Graves.
BTW, I wonder if Warner's arm would have been big enough for BA since BA's offense is built around the big passing play attack.