Rotten wood - front door assembly

I need some guidance with some rotten wood around our front door. We have a 20 year old townhouse with a metal front door and screen door. The wood between the screen door and main door is rotten. The brackets holding the springs for the screen door have pulled out of the rotten wood.
Is all this wood one assembly? That is, if I wanted to fix the rotten wood between the doors and install a new screen door, I?d have to replace the entire door assembly and main door?
The main door is in descent shape but is nothing special. One contractor I spoke with said it was easier and probably cheaper to replace the entire door and assembly then trying to cut out and replace the rotten wood between the doors.
Does anyone have any experience with this type of situation? Thank you for your assistance.
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