You need to provide more information. 5% on what? GrabDeals always has had different cashback % for different stores.
There isn't just one credit card in Axis portfolio and that's how advertisement banners have always worked. They have clearly shown an asterisk(*) and "T&C Apply" in the banner, that means there is fine print. There's always a fine print.
Again, missing information. 5% on which website? Where has it been changed to 1%? Add some screenshots maybe?
Both QwikCilver and WooHoo are owned by Pine Labs Pvt Ltd. so the merchant hasn't really changed. And woohoo has been their voucher vendor for almost a year now(I don't know the exact date but it has been a long time), it's nothing new.