Maybe it's not about a few percentage points but about it being a legit alternative. A few days ago it looked like Pfizer is in position to milk the market and now there is competition.
Pfizer's vaccine needs ultra-cold storage at around minus 75C, but it can be kept in the fridge for five days.
I think this is a big difference. I don't know if many hospitals and clinics, especially ones in remote locations, can have cold storage the Pfizer vaccine requires