Completely paint with wood filler?
I use a heat gun rather than chemical strippers. It's easier and usually all old paint can be scraped off. Heat guns do have their own set of special considerations and safety precautions but overall it is a better way IMO.

That being said, even if you remove all the old paint it is common to be left with a surface far from perfect. I use exterior grade spackle to skim coat outdoor trim prior to priming and painting. It dries quicker and is much easier to sand smooth than wood filler. The surface needs to be clean, and it sticks better when the wood is damp.

Wood filler is probably OK if it was applied correctly and sanded properly after application. Way too much work and $$ for me to use it, except for areas where a hard sub-surface is important like handrails, doors, window sashes; areas likely to be touched.