But for the light cruisers, speed is the main parameter. Slow light cruiser, it is just as questionable thing as unarmoured battleship (yes, I know about the "Lepanto" class. Exceptions prove the rule.)
Research shows that a speed of around 20 knots is not uncommon and still considered fast for the turn of the century. Check out the New Orleans Class from 1895:
http://www.navsource.org/archives/04/ne ... neworl.htm
She was built by the British, who understood speed, and the trial speed was only 20 knots on 3769 tons. Leons are two thirds the weight, and 75 feet shorter. The natural speed of her hull was only about 16 knots, and 18 was the most I could squeeze out of her. I also have a draft limitation of about 20 feet until they dredge the ship channel at the turn of the century
This AU runs on a budget. There's only so much money that can be spent in a year on defense. Right now, the strategic mission for this navy isn't fleet action, its commerce raiding. 18 knots is more than fast enough to catch most, if not all, merchant ships. The faster naval warships are owned by our allies.
There's also a limit to the number of men in the Navy. I can't exceed my manpower limit, so that factors in as well. It means a slightly slower ship, but when they go in to the yard for refit, they get new powerplants that often increase their speed.
I understand what you are saying in terms of tactics, but tactics only define the requirement.
Money and politicians decide what your navy actually gets.
Also, check these books out on Google Books:
Janes Fighting Ships 1900
Brassey's Naval Annual 1896
Warships of the World 1892
Warships of the World has an entire appendix on warship speed and the number of vessels that can make or exceed 20 knots at that time.
