a couple questions about sion

Hello guys today i played vs 2 sions , and in both game i was pushed under my turret receiving tones of dammage and he was tanking turret like its a minion -_- . I mean how it is possible to tank that hard and by the same moment deal huge ammount of dammage ? why sion is allowed to be tanky as hell and stack hp etc and deal lot of dammage ? ??
have they buffed him in the last few patches i mean i dont remember sionw as that strong last season