Co- witness is one of those pita things that won't go away.
With an absolute co-witness, the front, rear and optical sight are all in line.
This is a pretty poor way of doing business. The advantage of the sight- speed of acquisition- is lost when you are trying to line things up.
Question: How much time do you have in a gunfight?
Answer: The rest of your life...
If you want to spend time that may not be in the bank, you are free to look through the rear sight aperture, center the dot within, and then focus on the front sight tip.
That is not in my playbook.
A better method is to have the iron sight in the lower 1/3 of the optical viewing plane.
I keep my BUIS down, and the front sight is essentially transparent to me- i do not see it.
I have had a battery fail once (in 1995) and a sight fail once (earlier this year). Considering the number of rounds that i put down range, i'll stay with optics and not sweat the small stuff.
In the event of an optical failure at shortrange, the optic can work as a large ghost ring (within 15m). If farther out, i'll have sufficient time to deploy the BUIS.
The world is made for 20/20 vision. An astigmatism is a problem with red dots, but other vision issues shouldn't always be.
Keep both eyes open- that is the way the red dots were designed to work.
Flat tops are always a better option for optics as you have already found out.
Finally- kit guns are generally great for saving money. As my Dad said "You can pay now, or you can pay later, but you are going to pay".
My experience has been that those makers who are held contractually to a standard produce a gun that meets a standard. Those that don't have to meet a standard will take many shortcuts in the interest of turning a bigger profit by reducing overhead.
If your requirements are for a gun that you can shoot at a range a few times a year anything will do.
However, i have seen a great many kit guns, as well as those made by aftermarket companies puke in class.
Generally, the military and cop classes have less problems as the mil guns are all made by two companies that have to meet a standard. For cops, some have great guns, and some are garbage because of bean counters buying something "as good as" or "just like the real ones".
Buy cheap, buy twice...