The longer one has an extended version of Prost's interview in the middle somewhere which provides a lot of context to the film that otherwise wasn't there. That is perhaps it's most glaring omission.

For the third point, you might be confusing that with the incident Niki Lauda had where he walks out based on exactly what you said, rain conditions. (edit: this is covered in the movie "RUSH" by Ron Howard - which possibly might be the greatest racing movie of all time).

In the Senna film (not sure which version) Senna walks out of the drivers meeting after a heated discussion about going out on the shoulder of the track by accident (there was a run off area in the chicane so if you missed the turn you didn't go into a wall). Senna was penalized for that and I think ultimately lost the championship because of that penalty. While other drivers freely got away with the whole thing as the F1 President wasn't a very big Senna supporter and personal friends with Prost. Senna walked out of that meeting - while his fellow drivers were in agreement with him.

Unbelievably, the fucking F1 actually wanted Senna to TURN AROUND and GO AGAINST TRAFFIC just to get back on the chicane.

Edit: One other fun fact, Senna excelled at racing in the rain. Him and Schumacher would run laps around the entire field when it rained. You can argue about what percentage the car wins races over a driver but when it rained those two drivers clearly proved they were exceptional drivers regardless of the cars performance.