As far as I’ve heard, Ryanair will cut into literally everything (including comfort and decency) for the sake of efficiency – other than safety. Even if they wanted to, they're subject to the same commercial aviation regulations as everybody else.
Do you have anything other than this single incident to back up your insinuation that they’re less safe than a full service airline?
I don't know how true this is but I have heard Ryanair will use the absolute legal minimum amount of fuel whenever possible whereas other airlines might fly with a bit more.
In theory though that shouldn't matter because as you say, the legal minimum should really be enough.
That seems like a cost/convenience tradeoff: The implication of only carrying minimum fuel is that the pilots can't hold for long to see if conditions improve and instead have to immediately go for the alternate destination airport.
The consequence of that is everybody ending up in the wrong place, but not in an unsafe way.