Tachyons are obviously not the standard technology in this setting.
Especially not for a nation which would actually know how to use them aside from as a really-really convenient transmitter/weapon.
Tachyon is basically is a reference to particles moving faster than the speed of light.
As such even though this form of tachyon is rather "tame" compared what could it be, it's still energy and particles moving FTL, meaning electric fields or particles that only approach the speed of light are too slow with their disorderly movement and they don't appear to be an uniform "wall" against an FTL beam like they usually are.
This is why a tachyon beam passes through it with only minimal resistance.
Similar issue with armors. Even if they absorb radiation the individual tachyon particles are many times more energetic (if a beam is 500x FTL then 25,000 times more energetic) which means these can permeate classic radiation absorbent materials far better.
That's the brief physics behind them.
As for ZPMs, they are relatively rare but at least each of the more modern imperial warships have one as auxiliary energy system.
The main energy source for imperial warships and in general are via plasma generators.
These use plasma implosion to prepare the conditions for highly efficient fusion or antimatter reactions. But these can eventually run out.
Meanwhile the ZPM unit can provide less output and requires a large complex machinery to safely manage but it lasts for hundreds of years if not more.
Similarly, larger planetary worlds have emergency ZPMs in order to sustain themselves during grave situations.

You made comparisons to the IoM which is partially right.
I took inspiration from it, indeed.
But so I did with several others.
I'd imagine the average tech levels at somewhere the level of Star Trek.
There are many-many fictional alternatives to deal with this "dumbed down" tachyon beam.