OP's question shows lack of understanding of the purpose of abnormal procedures. Loss of pressurisation and loss of thrust on one engine has opposite aims to achieve. OEI in cruise you don't want to descent but have to because of insufficient thrust to maintain level flight so we do it with least ROD by locking thrust at MCT. In loss of pressurisation you want to descent as quickly as possible to ten thousand feet where oxygen is not required. So it can only be done at thrust idle, speed at MMO/VMO with speed brakes extended. Once the aircraft is settled in descent you can deal with engine fire to secure the engine and then complete EMER DES ECAM. After that switch back to engine fire items. It's unusual but not that complicated.