Resistor across output?
If the output has no resistor then transistor leakage will make it non-zero when it should be zero.
Also, the only thing discharging any load capacitance is the resistor (when the output should go from '1' to '0') so if the resistor is too high value the fall time will be very long, even if it eventually gets there.
This kind of textbook example gate is not great to learn from in some ways- they are not designed to be cascaded reliably with one output driving n (where n is the fanout) inputs regardless of the type (eg. AND, OR, NAND, NOR, X-OR) of gate.
This one has a diode drop from the inputs so cascaded gates have less output voltage than the input voltage, which eventually leads to something not working.
The simplest practical ecosystem of logic gates is probably the RTL logic that was made in the 1960s. From here. Power supply was typically about 3VDC.

Any gate can be made with a combination of 2-input NOR gates (or NAND gates). These ones had a fan-out of 16 (one output could drive 16 inputs) and there was a a uL900 inverting buffer that could drive 80 inputs.