I had my generator wired directly into my circuit box. I had a 30a 220 breaker, which matches the 30a breaker on the generator. (You get the idea: turn off the service breaker and as many other breakers as necessary; start the generator and turn on its breaker into the box. Not to code, but let's not get distracted on this point.)

For the wire I used three strands of #12 wire, with two wires each to the 220 poles and to the two grounds. I learned this from a friend and his father. Father was chief of maintenance at a big wood processing plant.

However, a guy who wired a new addition to our house mildly chided me on this. His argument was that unless the two mated wires to a given pole were of identical length, the current would only go down one. Makes some sense. On the other hand, an argument could be made that if that wire began to overload, it would create resistance and the current would flow down the other wire.

In rewiring, I used 10/3 from the box to an outside socket, but still using my old three strand from the generator to the socket.

Thoughts?

Sorry, but we have to provide answers that are to code. To do anything else would be irresponsible. The NEC is about safety, yours and others.

To begin with, you have created a potentially High voltage killing situation for any power company lineman with the way the generator is connected.
If you understand how a step down transformer works, then you should understand the inverse, a step up transformer works.

With your generator pumping out 7200 VA , if it reaches the panel and back tracts through the panel to the transformer, the voltage will be stepped up and continue downstream.

From my understanding of what I have learned here, the power company will trace backwards to find the source and cut all electricity to that source. They will not restore power to the home until an inspector has verified that the potential deadly situation has been corrected.

Your immediate next step should be to install either a manual or automatic transfer switch that breaks the circuit from the service line and then makes the connection to the circuit you need. You may have to set up a subpanel to interrupt the feeder from the service to the subpanel. But that is so much better than killing someone just to avoid code.

As to your wiring, you cannot parallel conductors that are smaller than #1 AWG. So your friend's work-around is fine for a very short duration in a manufacturing environment with trained service personnel in residence. It is not allowed in a residence.

#10, copper or #8 aluminum is listed for 30 amps.

Also something we really need to know is whether your generator is outputting 120 and 240 volts.

Here here donf. We lost a guy that way a few months ago.