Stainless bolts have a lower shear yield than Steel.
The minimum spec for a suspension bolt is 8.8 strength, an A4 stainless bolt isn't even close to that. Therefore stainless should only be used for non load bearing components such as trim, panels and expansion tanks etc.
Stainless bolts MUST be lubricated too as they are likely to sieze and if they dont then the steel component they screw into may corrode faster (galvanic corrosion) and cause the fixing to sieze solid.
The bolts do actually have a corrosion resistant coating, the problem is this is destroyed when they are removed. This is why you remove an untouched 10 year old bolt that looks new, then re-use it and 12 months down the line it looks badly rusted. It is also presumably why OEM's always recomend you use brand new bolts when replacing suspension components.
Alfa GT 3.2 V6 - Daily Driver.
Alfa 145 QV ph1 in green (Death by rust project) For Sale.
Alfa GTV TS ph2 in blue