Serious as a heart-attack.
So many folks, including our very own recent "2nd-greatest batsman" poll have Sobers as their 2nd greatest batsman of all-time. An honour that just isn't bestowed on Imran for his bowling. I've read the odd person who would have Imran as one of their top 5 bowlers at best, but mostly he seems to be in the top 10 if that high, and generally behind the likes of Marshall, Hadlee, Lillee, Barnes, McGrath, Steyn & Ambrose to name a few, and that's before even considering spin bowlers like Warne, Murali & co
In fact, is Imran he even considered to be the best Pakistani bowler of all time? Personally I'd give that honour to Akram, and I might be wrong, but I get the feeling most Pakistani cricket historians would too if we're purely talking bowling.
So in summary, Sobers is to many the 2nd greatest bat ever, and to most a definite top 5 candidate, whereas very few & none I've ever read rate Imran as high as number 2 bowler, and I don't believe most have him in their top 5.