[C Of K]

I'd still say the biggest points are in T1.
If T2 is such a valid movie, the Machines would have sent more than 1 terminator back to kill John Connor. That they sent only one terminator is a weak point in the plot for T2 and T3. This turned the series more into a display of superhero antics instead of the man vs machine story that was the original premise.

Only 1 terminator was sent in T1 because going back in time was a last ditch effort by the machines before the time machine was destroyed, and the war was won by the humans.