Looks like the parallel in ch. 2 is best explained as dependence on Revelation, considering that this chapter (along with ch. 1) is an interpolation into 4 Ezra also called 5 Ezra....The other parallel from ch. 13 noted earlier, however, is a basic part of 4 Ezra....
As for the possibility of a precursor to 4 Ezra, there are some interesting parallels between 4 Ezra and 4Q Pseudo-Ezekiel.