I rate him as the top 3 all rounders.Imran is a bit of a different case seeing as he did play as a specialist bat. It's very unfair on him as a bowler to include this period. I want to credit him for his batting phase too, as it makes him a better player, but it gets messy assessing him in different ways.
He's plenty good as a bowling AR without looking at his batting period. His average, runs, and longevity all drop, but remain excellent for a guy who is clearly a bowler first and foremost. But if you want to assess him as an AR on entire career, fair enough. At least this avoids the issue of people who will credit or discredit performances in one discipline based on agenda.
I see the point of not including tests where he played as a specialist bat in his bowling figures, but then he wasn't bowling in that last phase so it's get tricky to include that batting phase in all rounder phase, right? We can't say that let's remove the worst period for batting and bowling both to judge his all around contributions and then go back to cite 20 years of longevity and cite his entire volume of runs as an all rounder. I think it gets tricky.
I personaly don't think we need to take out 1 tests he played in first 4-5 years. 1 test is nothing. Or take out his bowling for the last phase when he was playing as specialist bat. That will only mess up his WPM but not his avg. WPM is anyway secondary after things like Avg. IK avg when he bowled less in later years is good as well. And when he did not bowl, it won't have any impact in his bowling avg.
If he had a huge decline as an all rounder like Botham then highlighting first part and second part tells us something new. Similarly, if a player has 80 tests of ATG performance then highlighting that stretch indicate the quality which we may miss due to stats declining a lot due to early years or later years. 80 tests are full career for most.
That's not the case with IK. As you said his case is comlicated, but his record is brilliant as an all rounder. Taking away this or that simply draws attention away from his actual great career record without adding much positive for him.