[Treeve]

That’s got nothing to do with quality of steel / fabrication and everything to do with the design of the A-arm and where the forces go. Failures like this are typical for a-arms where the shock is part way up the arm like that with a resulting bending moment. Designing for shock loads from potholes is easy and has been done for years (VSB 14 quotes similar numbers to those used by Lotus in the 1950’s for road cars... a bump is a bump is a bump).
A better solution is to change the force paths in the arm.
Treeve