There is a substantial difference between strobe lighting and "hot" lighting when it comes to measuring light output.
You don't specify which flash you are using, so I'll use an SB700 as an example, which if memory serves is rated at about 30watts with a 4/1 efficiency compared to an incandescent. So let's call it 120 lumen seconds.
The difference between the two is the rate at which it outputs the light. You'll notice that I used lumen seconds rather than lumens. This is because a strobe will dump its entire charge in a matter of milliseconds, so the entire incident occurs while your shutter is open.
Hot lights, on the other hand, are generally measured by the light they output in a full second. So for your 1750 lumen output, only 1/100th of that light is entering your camera. That is only about 17.5 lumen seconds during the exposure time.
Compare this to a 120 lumen second output from the strobe, and adding in the inverse square law to compensate for distance, it's very easily over a stop difference between the maximum output of your hot lamps and the lowest setting on your strobe (which is consistent with your sample).
That being the case, you're probably better off working to master single light setups (with reflectors) until you can afford to upgrade your kit.
Back when I was shooting, I did a ton of my work single source. I found the limitation forced me to be more creative. For example, this shot imitates the type of three light setup you're attempting with a single light source (the sun) with 2 reflectors providing the "key" and fill.