The high speed reels are better for reeling in large amounts of line per turn. This is obvious. It excels for techniques such as jerkbaiting, worming, jig and pigging etc., where slack line retrieval is significant.
Low gear ratios are better for high resistance baits, not because they retrieve less line per crank, but because they have more torque. Similar to the gears on a bike or a car; you start the vehicle in the lowest gear because it has the most torque to get the vehicle in motion. If you tried to start your car in 5th gear, you would likely stall because you don't have the torque to get it moving. High resistance baits are most often associated with deep crankbaits, although this could apply to big bladed spinnerbaits, chatterbaits.
So, you cannot actually get the effect of a lower gear ratio reel by simply reeling in more slowly - this does not change the physics. With that said, how many people fish super deep crankbaits all the time? For medium to shallow crankbaits, it is more about the speed and less about the torque. In which case, you can simply slow down a fast reel for thiese applications.
To your original point; the Curado e5 only comes in right hand retrieve. However, you can change the gears in a 201e7 to the 6.3:1 gears of a Citica to get a Curado 201e6. Otherwise, Consider offerings from Abu Garcia, Daiwa and BPS. Of these three, I own both Abu Garcia and BPS in the low gear ratios. My Abu is a c3-modded to c6 Ambassadeur 4600. This is a round reel with huge line capacity and the ability to cast ridiculous distances with big baits. If you don't like round reels, the BPS in question is the Pro Qualifier, and is a versatile, value reel that performs well beyond its pricepoint. It has dual breaking for changing wind conditions, and is available as low as 4.7:1 all the way to 7.1:1. Both of these reels can be had for less than $100. I currently use the round Abu since it casts so far, and there is something about using round reels.
I hope this helped some.
