It's kind of funny, people always question the metals that are typically used because of their soft characteristics, but never really consider that they can be made as a alloy as well. Titanium for example is considered to be a hard metal. It's not, it's actually very soft. It's when it's made as an alloy that it becomes so fantastic.
There are different grades of stainless steel, many are very soft. But when people typically think of stainless steel, they think of a nice durable hard metal. Most stainless steel grades are extremely easy to strip or cross thread. The brass 510 connection on this mod is plenty durable. Yes, you can cross thread it, but stainless steel is just as susceptible. This brass is very tough.