You are basically surmising there is no need for the wording at all times because your interpretation is it still means +15% to bleed effects other than just Thunderous Roar.
It’s unusual to see that in any spell/ability. No other spell says increases shadow damage +15% at all times.
Therefore, it’s perfectly reasonable to assume some sort of different interaction. If however, you with your access to Beta is telling me not, then thank you for confirmation.