The easy part is the part I'm best at.
Welding in new metal is the best type of repair, but quality body fillers are not a bad thing, assuming the metal underneath is well sealed. Typically someone just bondos over the rust, moisture is trapped, the rust grows, and the bondo falls off a few years later exposing a hideous cancer. But if you seal the rust and use a quality epoxy filler, it'll last as long as the rest of the panel.
I'm still getting better at that part, so this POR-15 job was basically a 'stop the horror' measure until I get better at the body filling part. And of course in non-visible locations like the spare tire compartment, battery tray, or trunk bed a repair like mine is perfectly acceptable, the black POR-15 holds its color well, and is a typical color for interior metal anyway.
peace,
sam