Severe Power Loss
 

1999 GDI Pajero Pinin. Started losing power intermittently. Sometimes my foot at the floor and almost no rpms. Heavy Misfiring. Eventually could not go up hills.
Check engine light codes read High Pressure fuel pump and Mass Air Flow Sensor. I ordered these 2 parts which took a long time to arrive. I drove short distances while waiting.
One day while driving i lost almost all power. Under 20 mph. Parts finally reached. i had them installed them. Had to also get a new throttle body. No more check engine light but still no engine power.
Catalytic converter clogged. My mechanic removed the exhaust manifold so the engine can breathe but still no engine power.
My questions are:
1. By disconnecting the manifold, should i have gotten some power back?
2. Where else should I attempt to look next for the problem please?

Thanks in advance to anyone with help.