I recall reading an article that mentioned -90C as the "safe shot", meaning they can be 100% certain that the vaccine is stable at this temp but it might be stable at much lower temps.
Also more BNT-XXX vaccines are in development.
I don't believe your logic follows. There's a lot riding on this vaccine working as advertised, thus there is considerable pressure on Pfizer/BioNTech to deliver on that promise. If they know their vaccine is at peak effectiveness when transported at -90ºC and that the effectiveness drops if handled at lower temperatures, and if time is critical as it is, then they have all the reasons in the world to just play it safe by going with the costly but reliable option.
Moderna's vaccine was the second to enter the US market. If Pfizer/BioNTech delayed their vaccine to work on lowering the temperature requirements, Moderna would eat their lunch, and Pfizer/BioNTech would be relegated to second place on the place it matters the most: the history books.
As is, I'm sure that Pfizer/BioNTech are already working on improving temperature requirements, while leading the race.
> This gives us three options, Is it Moderna taking more risks, Pfizer being more risk-averse or is the Moderna one inherently more stable?
I have zero insight on the situation, thus I can't really tell. However, it's clear that each and every single actor in the story, from biotech companies to politicians and also regulatory bodies, is taking way more risks on this issue than what they would otherwise take.