David Savitt and some REU students write about "harmonic curves" and "meanders". I have not read the estimates in details and I heard they can be optimized.
Harmonic algebraic curves and noncrossing partitionsHarmonic algebraic curves and noncrossing partitions
Polynomials, meanders, and paths in the lattice of noncrossing partitionsPolynomials, meanders, and paths in the lattice of noncrossing partitions
The idea is to check $\mathrm{Re}[p(x)]=0$ and $\mathrm{Im}[p(x)]=0$ and to show that they intersect at exactly $n = \mathrm{deg} \, p$ points. Then we can have a topological proof since we can split the plane into $\mathbb{C} \backslash \mathbb{D} \cup \mathbb{D}$ where on the outside we have an alternating series of lines extending out to infinity and inside we have some kind of non-crossing matching of the lines.
They come across an objection similar to what you have, is that topological picture correct? Can't the curves $I$ or $R$ be self-intersecting or worse?
Back then, there was no systematic study of shape such as topology. Savitt merely proves these curves are non-singular without explicitly ruling out these phenomena.
Then Savitt studies $\mathrm{Re}[e^{-i\theta}p(x)] = 0$ which contains $R$ and $I$ as special cases (set $\theta = 0, 90^\circ$)