I have been playing around with this for awhile. Then I went back to looking at e like this..The formula [imath] \pi(e^x)=\dfrac{e}{\sqrt[2]{e}}\cdot \dfrac{e}{\sqrt[3]{e}}\cdots\dfrac{e}{\sqrt[x]{e}}[/imath] means [imath] \dfrac{\pi(e^x)}{e^x}=e\cdot \dfrac{1}{\sqrt[2]{e}}\cdot \dfrac{1}{\sqrt[3]{e}}\cdots\dfrac{1}{\sqrt[x]{e}}.[/imath] If we assume that [imath] \pi(x)\sim\dfrac{x}{\log x} [/imath] then [imath] \dfrac{\pi(e^x)}{e^x}\sim \dfrac{1}{\log e^x}=\dfrac{1}{x} [/imath] and we have to compare the product of roots with the value [imath] 1/x. [/imath] Now the series expansion at infinity for the product of roots is
[math]\begin{array}{lll} \displaystyle{e\cdot \prod_{k=2}^n \dfrac{1}{\sqrt[k]{e}}=\dfrac{e^{2-\gamma}}{n} - \dfrac{e^{2-\gamma}}{2n^2} + \dfrac{5e^{2-\gamma}}{24n^3} -\dfrac{e^{2-\gamma}}{16n^4} + \dfrac{47e^{2-\gamma}}{5760n^5}+ O\left(\dfrac{1}{n^6}\right)\approx \dfrac{e^{1.423}}{n}+ O\left(n^{-2}\right)\approx\dfrac{ 4.148655621}{n}+O\left(n^{-2}\right)} \end{array}[/math]
This means that you have a systematic error of a bit over [imath] \dfrac{3}{x} [/imath] in your formula. This becomes smaller with larger values of [imath] x. [/imath] Nevertheless it is an error. [imath] \gamma \approx 0.57721\ldots[/imath] is the Euler-Mascheroni constant, defined as [math] \displaystyle{\gamma= \lim_{n \to \infty} \left(-\log n +\sum_{k=1}^n\dfrac{1}{k}\right)}.[/math]
You should divide your formula for [imath] \pi(x) [/imath] by [imath] e^{2-\gamma} [/imath] to get an error of the magnitude [imath] 1/x^2. [/imath]
1+(1/n)^n. It seems like if you multiply n by 2 you get a very good approximation for what we were playing around with earlier.

Any thoughts?
Edit. It should be the n-2 that gets divided by 2. Sorry