I think the third condition is true conditional on Schanuel’s conjecture.
Here is an example of using Schanuel’s conjecture to rule out the possibility that $e$ is the solution to $2^{2^u}-u=93$. I hope and expect that this (or some simplification) provides a template for ruling out all possible existential definitions of $e$.
Consider the four pairs of expressions:
$$w=\ln 2, \ e^w=2\\ x=1, \ e^x=e\\ y=e \ln 2, \ e^y=2^e\\ z=(2^e) \ln 2,\ e^z=2^{2^e}$$
We have five independent algebraic relationships among them:
$$e^z - e^x = 93\\ e^w = 2\\ x = 1\\ y = w e^x\\ y e^y = z e^x$$
By Schanuel’s conjecture there must be a rational linear dependence among the first four variables:
$$a w + b x + c y + d z = 0$$
and dividing by $\ln 2$ gives
$$a + b/w + c e^x + d e^y = 0$$
So the three pairs of expressions with $w,x,y$ have four independent algebraic relationships between them:
$$a + b/w + c e^x + d e^y = 0\\ e^w = 2\\ x = 1\\ y = w e^x$$
By Schanuel’s conjecture there must be a rational linear dependence:
$$p w + q x + r y = 0$$
and dividing by $\ln 2$ gives
$$p + q/w + r e^x = 0$$
So the two pairs of expressions with $w,x$ have three independent algebraic relationships:
$$p + q/w + r e^x = 0\\ e^w = 2\\ x = 1$$
By Schanuel’s conjecture there must be a rational linear dependence
$$s w + t x = 0$$
which means $\ln 2$ is rational, which is impossible.