Oh no, her forehand was a weapon, especialy for her time. Remember almost all the women were serve and volleyers in her prime so the standard of groundstrokers was not that high to begin with. Now compare her groundstrokes, especialy her forehand, to the top 10 of the time- Shriver, Durie, Bunge, Potter, Turnbull, Garrison, Kohde Kilsch, Rinaldi, and you will see what I mean. She easily had one of the best forehands in the game, and even Chris Evert called it a huge weapon and said she feared that shot. Here is Martina WAY past her prime, and her forehand is doing quite a bit of damage in her match vs Seles at Wimbledon 92 (and again this is Navratilova in mid 30s at like 70% of her prime level at most, the fact she is losing to Seles on grass which no way in hell would ever happen to prime Martina proving my point, LOL):
Navratilova even won a lot of forehand exchangs against GRAF in their 86-89 matches. That already tells you she had a very good forehand. And she was able to use her forehand to win quite a few baseline exchanges with Chris, or get into the net easily to set up easy volleys with it vs Chris.