By the time Fascism comes along, most of my land improvements are done. There are still some rails to lay, but that's about it. If I want double speed workers I'd rather spend my time researching Replaceable Parts. I usually have quite an army of slaves to finish with the rails so worker support and speed doesn't tend to factor in.
Republic's commerce bonus easier pays for most of the additional unit support while supporting a significantly higher science rate.
Republic is simply more flexible than Fascism. You can't make much use of gold in Fascism. It just sits there. Early in the Industrial Age, I turn off science and rush buy a bunch of factories in my core cities. Some of those go on to build coal plants. Now I've almost doubled my production in a much shorter time period than possible under Fascism. I can now easily nab Women's Suffrage which takes care of most of your WW problems. Likewise, I can turn off science for a few turns and generate gobs and gobs of gold for upgrading to infantry.
For war, Republic lets you rush temples, barracks, harbors, airports and units wherever they are needed. At peace, sell your techs to the AI for generous amounts of gpt. This kills their research and gives you more gold yet again.
For a long war, you're better off switching but I don't think I'd pick a government that kills off a good portion of my population.
