Can a hybrid bike's stem be slammed to make it nearly as fast and powerful as a road or cyclocross bike? Can a hybrid bike's stem be slammed to make it nearly as fast and powerful as a road or cyclocross bike?

More aggressive positions are thought to improve power transfer. That means a better workout when doing HIIT.

With a lower position, we tend to be more aerodynamic. People often find that road bikes are a few km/h faster than hybrid bikes. A cyclocross bike isn't much slower than a road bike. It must be mostly aerodynamics that played a role.

Someone might want to do this because it's cheaper and prefers handlebar mounted shifters. A pair of STI shifters can cost a few hundreds of dollars while equivalent speed shifters may cost only one third that for non-drop style handlebars.

According to the following article, it looks like we need to select a stem with an angle and length that makes the handlebar height 5 to 10 cm below that of the saddle.
https://www.mec.ca/en/explore/fitting-your-bike

If I use the right stem so that the reach and handlebar heights are similar to those of road bikes, would it work? The stem may need to be longer than you can find in stores because there are no hoods to extend the reach.

Photo of my bike. The bike fitter used a long stem for a performance fit.
There is no absolute 'correct' way to get a lower more aggressive position. 

You probably can get a lower, more aggressive position on a hybrid bike by adjusting the stem angle and length, but how much lower depends on the inherent stack and reach geometry of the frame. You are also limited by flat bars which obviously do not have the drop sections that allow a very low position. Flat bars tend to be a bit wider than drop bar hoods which also compromises how aero you can get.

There is not a magic vertical distance between the seat and handlebar, so forget the 5-10cm measurement. Just experiment with what you can do on your bike, and what works for you. 

If you can get a significantly lower bar position, you may need to pull the saddle forward a little. Bikes with more upright riding positions typically have a slacker seat tube angle that puts the saddle further behind the bottom bracket.

Update added a few days later:

Be aware you are very unlikely to make your hybrid 'nearly as fast and powerful as a road or cyclocross bike'. The riding position is not the only factor. Hybrids have other design features that sacrifice speed for comfort and lower price: wider tires, lower gearing, heavier components, less stiff frames and wheels etc.