I think you are on the right track.
TEAW - Turns are 15 days and the war goes on from 1914-1918. Thirty Years War is turns of 30 days and goes on for well, 30 years, 1618-1648. The first few turns of TYW (I will use abbreviations from now on) go by very quickly because it is mostly a small rebellion at first and not many decisions to make. TEAW the first few turns take a while, if you ask me, because you need to go through all units. Decide on build strategy. Decide on a lot of different things.
I am not sure if they use exact same engine, but I think so.
If you want a good example of differences between the two, watch XTRG's let's plays and some of his TYW Let's play. It will show you much of the differences. A lot more "economic" juggling is in TEAW. Largest battles I have seen in TEAW involved 1.5 million men total both sides. So far largest battle I have seen in TYW has been about 35,000 men total both sides.