Been there, done that.
In-tank fuel filters are good at doing exactly what they were designed to do: Get the vehicle through its warranty period. They're screens designed only to keep big junk out of the pump itself.
Less than perfect fuel is a fact of life. Especially for a person who travels outside of the beaten path, choosing familiar fuel stations is simply not a choice.
The poor fuel filtration should not, and does not cause complete fuel system failure. It just causes injectors to operate poorly, which is something most people never do anything about.
An OEM addressing their pathetic filtration is something that is not heard of much outside of the diesel engine world. Gasoline engines are far more forgiving to dirty injectors. They just cause drivability issues for the most part. They rarely result in engine destruction. But the fact is, OEMs have been caught with their pants down on this topic.
The idea that an inline fuel filter is going to cause undue restriction is ridiculous. There are very few fuel systems that will ever expose a fuel pump to open flow volumes. I've used inline filters in fuel systems that have to pump gallons per minute. The filter simply needs to be selected for the flow of the system.
Every single automotive engine marinized for marine use has an inline fuel filter, and surprise! They live long and happy lives.
On our Cummins engines, we add not only one additional fuel filter, but two inline filters (2 micron CAT filter, and filtering water separator) on top of our stock dual-media filters, and no injector death occurs with our far more sensitive injectors.
Since I always have cases of spares around, I use Volvo Penta Marine 6-micron spin-on fuel filters on the appropriate filter heads. Nice thing is, they are water separators too.
Of course, whenever I feel like it, I can just get under, spin the old one off and spin a new one on.
Flow? No problem feeding a 400+HP V8 engine, running at 4000+rpm for hours on end.
Filtration? I've pulled old VP filters off of engines that were running fuel so saturated with contaminants that rust was caked up on the base plate. Clean side however, was perfectly spotless as were injectors.
It's not rocket science. Just cut your stock fuel lines, flare a little, and use appropriate sized hose to connect to appropriate sized fitting on the filter head. Same way it's done when going CAT filters on a diesel truck.
Your mechanic is simply exercising good judgement.
