I do a lot of work in this area (my most recent project was 3d printing a mold to make a silicone mold to make a reece's peanut butter cup) and he's totally wrong about filament not being strong enough to act as a load-bearing bracket, given the size he has. Most people would just increase the fill to 100%, but that's not the way to increase part strength. Instead, you increase the number of horizontal and vertical walls. I would also avoid PLA (strong but degrades quickly and has wonky failure modes), instead using ABS or (my preference) PETG.