Randuin and frozen heart buffs on PBE are actually nerfs for Ashe Q I just saw this amumu taking 0 damage on ashe Q on the main sub and realised that with these buffs Ashe Q will do even less damages next patch.
For reminder currently randuin and frozen heart reduce incoming damage by a flat 0.5% of the owner life, it goes to 5 + 0.35%hp for randuin and 10+0.35%hp for frozen heart. 
Ashe Q hit 5 times per auto. 
For example with a bruiser with 2000hp max it goes from a 10 flat reduction to 12 for randuin and 17 for frozen heart which becomes 60 and 85 on ashe Q of flat reduction, and there is armor and even tabis.