Relation between velocity of a electron (In the Bohr model of the atom) and the radius

A proportionality is meaningful only in a certain context. In the context of a single atom, the quantities $Z,m,e$ are constant and $n,v,r$ are interdependent on each other.

In the context of a single atom, the second proportionality is not correct because the value of $n$ is not constant (different values of $n$ correspond to different orbits). $$v=\frac{nh}{2πmr}⇒v∝\frac{n}{r}$$ The first proportionality is correct in the context of a single atom of one element; however, if you are analyzing many elements, $Z$ is also a variable. It too becomes incorrect.