I'm curious, with a transistor being equivalent to two diodes, could one wire a single PNP with a pull down diode to be an OR gate? My thinking is as follows:
Is this right, or wrong. Why?
Figure 1. A tidy version of the OP's 'OR' gate.
It might work in certain circumstances. The problem is that the base current affects the emitter-collector resistance.
It's not going to work as you planned.
Figure 2. Simulation circuit.
Running a simulation using the CircuitLab tool results in the following readings for R1 = R2 at 1k and 100 Ω:
1k 100 Ω A 1.927 V 2.469 V B 1.909 V 2.365 V Q 1.163 V 1.663 V
Note that at lower source resistance the effect of R3 is less and A and B settle down close to mid-supply. Q is 0.7 V below the emitter voltage as would be expected.