Insurance against a launch monopoly would be more effected by competition in general, no need to build your own rocket. I have also never heard anybody from ESA make that claim.
Ariane 5 is reliable but the primary reason it is launching rather then ULA is not reliability but politics.
> Ariane's goal is not to win the most commercial contracts or compete with SpaceX on price.
That is false. That was exactly what their goal was all the way up to a 1-2 years ago when they finally realized how badly they fucked up.
They spent the last 10 years laughing at SpaceX and telling everybody how stupid SpaceX is and how nothing is gone work and how much better they are.
> This is also the reason reusability doesn't make sense for Ariane. With less than ten launches per year, fixed costs make up a large portion of the cost. If they only needed one rocket per year, it wouldn't really get all that much cheaper because they still need the factory.
You are repeating what is essentially propaganda that ignores important facts.
The reason Ariane can only launch 10 times a year is because they totally failed in innovating and rested their success for a long time and now that they got 3 billion to develop a new rocket, that they claimed would be competitive. However the totally fucked that up and are not even close to being competitive.
The very reason they go all this money for Ariane 6 was to build something competitive so they could continue to capture commercial launch so that government flights were cheap.
So it is not that re-usability is not worth it, its that they failed to make a commercially viable product and without that they are just monopolistic launch with a low launch rate.