This is likely the biggest technical problem. You don't have good connection with the legs to the handle. However there are likely many others. Take a video.Another possibility is "shooting the slide."...
You should be able to row almost as fast without pulling much with the arms at all. You legs should hurt more then your arms.
A drag factor of 118 is plenty high if you have good technique. Heavy weight world records have been set at a lower drag factor.
Drag factor changes should only make a difference of a few seconds per 500m.
There are a lot of very good coaches who disagree with this. Most world class rowers do most of their rowing at low ratings. If you are a masters athlete doing low to moderate mileage then maybe you can get by with out it, but rowing at low ratings with powerful strokes builds muscle endurance as well as developing mitochondria and capillaries. A slow relaxed recovery also gives one time to think about technique and prepare for each stroke. It is much easier to change a bad habit at low ratings.I don't think there is any great merit in low pull rates.