Yea. It is a *galactic* civilization after all.
I will mention that most of it is tied up simply in patrolling and keeping an eye on space, which there is a lot of, meaning they can't deploy too much at once without losing control elsewhere. Hence you're more likely to see a few dozen at a fight than a big number (also, I will note that the numbers are largely based on just how big a galaxy is- 'few dozen, maybe a hundred or two at a particularly huge battle' is about all you'll see on screen or page at once).
Consider Return of the Jedi- that wasn't nearly the entire Empire fleet, that was just what they could use in a trap without tipping the rebels off, i.e. they had to leave their forces elsewhere intact enough to not raise eyebrows.
It had, the Executor, 30+ Star Destroyers, and a good number of smaller ships.
The Rebels had almost as many capital ships, though theirs tended to be smaller.
So in other words, in the one battle, there were more forces deployed than the 39 dreadnaughts the Turians had.