It most certainly was the case. How many times were they able to call in reinforcements, outside of ERRAND OF MERCY (which is one where the showdown was already coming before the show started?) Usually the Enterprise WAS the reinforcement in response to a call if they were local. But you have plenty of shows like RETURN TO TOMORROW and I believe SAVAGE CURTAIN where they are operating weeks away from Starfleet, even by radio. That is the frontier, and that is the aspect ModernTrek really lost (even though according to their guide it was still only a sliver of the galaxy that had been explored -- instead of TOS' 4% it was 11 or 17% wasn't it?), especially with their ships seemingly outclassing most would-be opponents. The premise of the show has been called near-anthology, because you could do all kinds of shows; but if you lost the frontier aspect, you lost the principal hook. It's like when you go from the old west to the horseless carriage ... you have a short time of extreme interest when the old generation has to try to adapt to the new more boring ways, and then you have a much less interesting area in terms of drama (at least till world wars start.) That's why the biggest miss in Trek history (outside perhaps of Lil Enterprise and not really SHOWING how we bootstrapped our way up after ww3) is not doing the era the movies were entering, the end of century, when you would have the real transition from TOS to TNG begin happening.