If a Planet is retrograde it isn't weaker, it means that its energies affect our Soul in a different way than a direct one.
Even if Taurus is Mars' fall Sign, thus debilitating it, it is actually a good placement. It makes you proficient in obtaining money, passionate with your partner, constant and diligent in your affairs and projects (the fixed earth sign of Taurus is a great helper in keeping the flaming energy of Mars under control).
However the retrograde motion can brings some problems like: holding too much back your anger with subsequent rage explosion, poor sexual drive (like Mars in Libra), general lack of vitality.