Well, Andy, comparing detonation internal combustion engines, no matter the fuel, is comparing one fundamental technology in various cost regimes.
Jets (and TurboProps) and turbines are a second technology of the same basic principle: fuel detonation. One which is useful in certain limited regimes. Most of which are NOT on the ground.
Props are essentially, now, only for sporting planes and puddle jumpers, where speed is NOT an issue, and can be a liability.
It's really more like the difference between Air-Rafts and Small Craft. Both will get you to orbit... but you'd be hard pressed to make Venus from Earth in the Air/Raft, even the enclosed ones. Both use the same fundamental technology: gravitics; different expressions thereof. (At least, they do under MT...) Different regimes of the same fundamental technology.
Now, compare lift systems: we have three basic lift systems. Vectored thrust, Airfoil, and Air Displacement (Lighter-than-air). Only one is practical overall: airfoil. 99%+ of aircraft use airfoils. Birds, Bats, and Flying-Fish all use airfoils.
AS far as I know, Nature hasn't used displacement in the air. It does use it a variety of aquatic applications...
Insect flight mixes vectored thrust and airfoil... due to scaling issues, smaller insects actually are more thrust than airfoil. Big critters, however, use Airfoils.
If it moves, we generally lift it into the air by airfoils. If it loiters long term, we lift it by displacement. Short term, we still use Airfoils most of the time (Helicopters move their airfoils, rather than moving the whole plane).
As of late, we use Magnetics to lift things a very small space... but unless some element changes, MagLev is likely to remain a tight niche.
We have three major branches of thrust, but all three are reaction drives. Ionized Gas Accelerators, Chemical Combustion, and Thermal Expansion. (A 4th, pressure release rockets, are mostly just novelties.) All work by accelerating a working medium out the back. All have particular regimes in which they work best. Chemical is awesome for high thrust, short duration. Thermal Expansion drives (often called resistojets) are used for very light duty, intermittent, single propellant applications, like satellite RCS systems; a new regime is being proposed for this application, using really high temperatures, and air as the expanded fluid... but they still are one fundamental technology: expanding gas going out the -z to push you on the +z.
Light-pressure propulsion is proven possible... but it is really dwarfed even by the miniscule thrust of Ionized gas drives. Solar wind is also doable... same deal. But, the two combined have some promise, but the new generation of ionized gas/plasma accelerators looks to put them back into the "Not worth it category."
Bab-5, for example, postulates a SINGLE underlying technology, with two different ways to use it. Both Gates and Jump Drives (in the B5U) simply allow you to open portals to/from jump-space.
Trek's various drives all seem based upon different applications of a single "subspace theory", save wormholes, which are possible under many current theories, but not practical, unless all you want to do is send radio. Plus, we see a generation ship in TOS... Yonoda... and TNG. But those two are special cases; one is sublight... they didn't have warp. The other is a generation ship not due to lacking warp, but because it's refugee-filled.
When looking at multiple star-drives, ask yourself: Are these really two separate approaches, or different regimes of ONE approach. If they are separate regimes of one approach, it is far more likely to see them remain in parallel use.
If they are two truly different approaches (EG Stutterwarp and Jump Drive, or Stutterwarp and T-plates), due to similar regimes, only one is likely to predominate. In the case of M-Drives, the Stutterwarp has it all over the T-plates. In the case of FTL, it depends upon the tech paradigm.
Taking that last back up... If merchants pick Jump, it makes it harder, but not impossible, for the military, to go SW, at least as an MD. But if the merchants go SW, the military WILL follow, if only to do literally that... follow and harrass, follow and escort. They might ALSO mount J-Drives, but if they do, non-JD ships will have a huge mass/volume advantage.
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