PLA is not "quite weak". In fact, PLA's tensile strength is the highest of the easily printed materials (so excluding nylon and polycarbonate). Typical printed tensile strength of PLA is 40-60% higher than PETG, for example.
PLA is also stiff, among the stiffest of common printing materials.
Yeah, PLA, if you anneal it and use the right grade, has a strength to weight ratio the same as common Aluminum 3003 alloy, about 50MPa/(g/cc), which is also about the same as standard strength steel.
I do not have any experience using pla in an industrial setting. When talking about 1.75mm filament one can buy on a roll for a basic 3d printer, I can say I've printed a number of PLA things at 200-215C with appropriate slicer settings, speeds and such for beautiful looking output results, but all of them can be easily snapped in half by hand if I try.
PLA in the context of low
cost consumer fused deposition 3d printers is quite weak, compared to other filaments that can work in the same printer, such as abs.
For something like a $300 printer you generally have a choice of pla, something like sainsmart tpu for semi flexible, and abs if you can print with ventilation.
PLA is also stiff, among the stiffest of common printing materials.