9 G's could be deadly if injured people are on board
The Soyuz is a proven design and is performing valuable service to the ISS. However, a 9G reentry could be more than just uncomfortable if injuried people are on board. In that case, it might not make the best long term solution for an ISS lifeboat. I'll have to see if I can find more info to see if this was an exceptional case or is closer to the norm for a Soyuz reentry.