I would think greater physical strength would be a massive help and since males already have a good amount of testosterone their bodies might be able to handle the extra they receive from the mutations. However I wasn't talking about just strength, I meant that the mutagens were specifically made for males and since men are generally stronger than women, the mutations may be too much for their bodies to handle
I don't recall being mentioned that mutagens were made specifically for males - in fact, becoming the Witcher is not just a matter of living through just Trial of Grasses, but a continuous process that takes years of ingesting various types of hormones, mutagens and else. Probably somewhat personalized as well.
And while women may not possess as great physical strength, they're actually more resilient (Outcomes Research at the Johns Hopkins School of Medicine, found that women who had suffered traumatic injuries were 14 percent less likely to die after surgery than men with equivalent wounds and experienced fewer complications during recovery).
You HAVE to be to deal with the ordeal of pregnancy and childbirth, you know?
They're also more resilient to many diseases and less prone to have faulty genetic mutations than males - a factor that may prove beneficial when going through years of "Witcheryfying" process.