If Johnson was innocent of misleading Parliament then he would want an investigation as soon as possible. The fact that he is seeking to delay an investigation for as long as possible is a sign of desperation.
The police investigation, and the Sue Grey report have nothing to do with the charge that he lied in Parliament. The Police and Sue Grey have not investigated that, so it makes absolutely no sense to wait for those to be concluded.
What Johnson is doing is running away, hoping that people will get bored of the matter and let him get away with it. Misleading Parliament is a serious charge, not a piddling fine. The ministerial code says he should resign if he is guilty as charged. That is why he wants to delay, delay, delay.
(There was always something fishy about the Sue Grey Report being suppressed at the eleventh hour).