Errors in Einstein's Reasoning (1)

In his original paper [1], why did Einstein use the word "stationary"? Let's have a look at the first step in Einstein's paper:

first step in paper

What does it tell us? There must be a stationary reference frame where we can get c, and there must also be a non-stationary reference frame where we can get c+v and c-v. In addition to that, light must follow the rule of relative motion, as c+v and c-v are all obtained from Galilean velocity addition rule.

So our interpretation of the second postulate is wrong. Although we do not know where to find this stationary reference frame, it must exist. The speed of light used in Special Relativity is relative to this reference frame only.

If we follow this route, then all the paradoxes will disappear, as the conclusions of Special Relativity are valid either in a "stationary" reference frame, or in a moving reference frame, but not in both.

But wait a minute. The principle of relativity seems to be unnecessary. If it is present in his paper, Einstein certainly had use for it. It seems we get lost again.