If $\pi(x) > \operatorname{Li(x)},$ is $\vartheta(x) > x$? Are the two inequalities (solutions to both of which are known to exist but not known exactly) equivalent, similar, or mostly unrelated?


$\vartheta(x)$ is the [Chebyshev Theta Function](https://en.wikipedia.org/wiki/Chebyshev_function).



Bounds on $\pi(x)$ vs. bounds on $\vartheta(x)$
One can address this problem using tools from comparative prime number theory ("prime number races"). Assuming RH, the (logarithmic) limiting distribution of the vector-valued error function
$$
\bigg( \frac{\pi(t)-\mathop{\rm Li}(t)}{\sqrt t/\log t} , \frac{\theta(t)-t}{\sqrt t} \bigg)
$$
is supported on the diagonal $y=x$ in $\Bbb R^2$; with further assumptions on the imaginary parts of the zeros of $\zeta(s)$, that distribution will not assign the origin any mass. Consequently, the two inequalities are either simultaneously true or simultaneously false for all $x>0$ except for a set of density $0$.


It's unthinkable that the real number where $\pi(x)$ crosses $\mathop{\rm Li}(x)$ will magically be the same real number where $\theta(x)$ crosses $x$; that's what would be required for the pair of inequalities to be perfectly correlated. Even if you restrict $x$ to be an integer, it's still extremely unlikely. For instance, any theoretical argument that linked the two inequalities should also link the inequalities
$$
\pi(x;q,a) > \frac{\mathop{\rm Li}(x)}{\phi(q)} \quad\text{and}\quad \theta(x;q,a) > \frac{x}{\phi(q)}
$$
concerning primes in arithmetic progressions; yet examples where one such inequality holds but the other doesn't are easily found by hand.


