No, he's not very injury prone, it's a myth only in one of his 5 seasons has he played less than 40 games. In 5 years he has played 150 league games 208 total. Take out 13/14 season when he only played 34 games and his record is as good as any bodies.
From
www.transfermarkt.com:
15/16 Malleolar injury Apr 11, 2016 Apr 11, 2016 0 days -
15/16 Calf Problems Apr 11, 2016 Apr 11, 2016 0 days -
15/16 Minor wound Feb 18, 2016 Feb 22, 2016 4 days
15/16 Wound Nov 30, 2015 Dec 14, 2015 14 days
15/16 Hamstring Injury Oct 12, 2015 Nov 19, 2015 38 days
14/15 Ligament Injury Dec 8, 2014 Jan 8, 2015 31 days
Seems pretty injured over this last season and a half to me.
Agreed though about his goal scoring record - it's phenomenal.
Edit - A title-winning EPL side can afford to lose about 4-6 games. If Kun is injured for 6 games, and is say recovering for another 3 or so, that means that our backup striker had better be really good - or we just need to totally dominate the rest of the league and our staring striker doesn't matter. Given Kun's injury record - I really think we need a 2nd really good striker to help ensure that we'll win the league.
And if we only have Kun and Nacho - we'd really better be Barca/Bayern/Madrid class to win the EPL IMO without a suitable replacement - yes a winger/midfielder might fit in... but the striker position is special. Often the stiker poses such a big threat that the wingers/midfielders/other forwards are left open to score - Kun out is huge, Kun and Nacho out without replacement might well be title ending IMO.