Is it sufficient to cycle out brake fluid as opposed to "replacing" or "flushing" it?

There's one slight problem with your theory. The fluid which goes out to the brake cylinders/calipers stays out there. It will never come back to the master cylinder. You have to do something to remove this fluid. The only way is to flush it out.

The biggest issue with all of this is the brake fluid which never comes back and stays in the lines will absorb water over time. The water will then act to cause corrosion on the steel brake lines. Sooner or later it will rust through and have issues. If you don't flush them, it will have issues sooner or later.

As an aside, the normal change interval for brake fluid is two years, regardless of mileage. After that it will usually start to change color. The darker it gets, the more water it has absorbed.

Your method is alright, don't worry, it will mix, but you have to drive a few hundred miles before next change.

I did it myself long time ago with Brake Fluid Tester showing my old Brake Fluid was at least at 4 % of water contamination.

I tested the new bottle DOT-4 it was 1% (inside the Bottle) then I sucked up all Reservoir fluid (all of it ) and then poured the new DOT-4. After 1 week of driving (high-ways and city traffic), I re-tested my reservoir, guess what: it was 3%. This is evidence that the fluid will be mixed. I then repeated the process until I got 1% of water in the reservoir,

By the way, don't worry about air if you sucked all the reservoir, because the master Cylinder just below it will be full of fluid and no way the air enters it. When you pour the new fluid into the reservoir, the air in the reservoir will be expelled automatically.

I have suffered from old Fluid where I lose brake sometimes, especially in the traffic in summer, but now it is alright.

I sucked out ALL the old green coloured fluid from the reservoir and replaced with new clear Toyota Dot 3, without bleeding. After just a couple of miles driving, the clear fluid in the reservoir turned slightly greenish. The next day I drove 20miles and observed that the fluid had turned even more greenish. These are evidence that fluid in the reservoir is circulated and mixed with old fluid in the lines below. The idea that fluid in the lines are stationary is not correct because the pumping action as the brakes are depressed and released generate hydraulic movement that circulate the fluid throughout the entire system. Even when the vehicle is not being used, diffusion alone will eventually mix the old and new fluid together although the process will take longer.