> Plus most instruments on ESA nmissions are sponsored by their implementing institutions e.g. Universities, not ESA.

This is true. Regrettably. The instruments are often built using public money and the platforms they sit on are almost always launched using public money, but the affiliated universities get to restrict everyone else's access to the data for years.

I personally know people working at ESA who were denied the right to publish their work and whose conference talks (in the area of interplanetary navigation) were censored by their managers because it was feared that they would reveal too much information which could conceivably be used by scientists from unaffiliated institutions in their research.

Open access is not big in ESA at all. This is a complete opposite of NASA's commitment to keep all data acquired with public money open to the public.