Sorta? But the question is so closely linked to one's definition of "complexity" in a game as to be kinda meaningless.
Chess is a stupid game. It implies that a battle is fought on equal sized armies, same composition, absolute knowledge of enemy positions, clear terrain, top morale, top discipline and the king is present....
Moreover there is no luck involved. Thousands of battles have been lost due to bad luck. Imagine in chess that your queen can't move this turn because she is sick...
No battle is ever that fair. In eu4 you control all these + diplomacy + 100000 more things.
I think the main difference is that chess is a game of complete information, while EU4 (and real war) is a game of incomplete information. So the complexity in EU4 is greatly increased by the fact that you must make up possible scenarios for what you can't see.
This would be true if you knew what your opponent was thinking. You can see all the board, but since you only have one move per turn, you can only act so much on that information. This, of course, is assuming that players even bother to take a look at the whole board before making a move.
Ok, chess isn't that complicated. It is simple enough that computers can beat grandmasters through brute forcing every possibility. In fact, after the first few moves (2 or 3 I believe) chess has been solved.
Not just this. I was saying that there is a relatively small amount of moves your opponent can make every turn, while in Europa Universalis there are almost endless possibilities.
Comparing Europa Universalis IV and chess game is like comparing apple vs. orange. I don't think it's possible to compare those two.