Perez drove an entire lap while going deliberately slow in every corner of sector 3 in Abu Dhabi and didn’t get penalized. Hamilton didn’t bin the car either. Considering that, there is no way this penalty is justified.

FIA being inconsistent is the norm. Last year Norris got a penalty for driving slowly despite not really obstructing anyone. If you want my opinion, then Perez should’ve also received a penalty.

What if Alonso had a sudden PU issue slowing him down¿? Would Russell still blame Alonso for the crash when it is his responsibility to react and maintain control¿?

If he doesn’t get off the racing line, yes. The first thing any driver does when they have a severe PU issue is get off the racing line. Just like Russell should’ve had time to react, in this hypothetical scenario Alonso would’ve also had time to react and get off the racing line. Alonso should’ve received a penalty even if it was a PU issue that caused him to slow down that much.