Fastpass at Disney is a double-edged sword. In the case of Thunder Mountain, the Paris version allocates one station to Fastpass and the other to Standby. Fastpass therefore doubles the Standby wait time. I don't remember how the other Thunder's run but there are examples such as Radiator Springs Racers, Soarin' and Test Track where the high amount of Fastpasses allocated can really slow down the Standby queue. To be fair, it has improved compared to when return times weren't enforced.
Europa do check restraints on rides that need it and if they think you're not secure or mucking around they will slam them down.