Read what I said more closely.
It is unrealistic if you use the parsec as a measurement for 1 combat square.
It is quite possible that the engines are sublight as it takes light only a few hours to travel from the sun to the outer limits of our solar system. The systems in SE4 are 13x13 grids. Thus to travel from one edge of the system to the other in a single game month is possible with the fastest ships at sublight speeds, indeed at just a few percents below light speed you could do it in a few hours.
Sun to Pluto 5.4 hours
So 5.4 x 2 = 10.8 hours to go from one side to the other.
A parsec on the other hand is just over 3 light years in distance all by itself. Move several of those in one combat turn, one combat turn being a small measure of time (some minutes or hours) and you have much faster than the speed of light for engines.
Quite unrealistic.
I was simply stating that a combat square is clearly not a parsec. Hope no confusion resulted from that.