You're talking about advertising, which is only one aspect of marketing—and fyi I have no experience with TV ads, radio and magazine were as far as we tried offline, and not in any major way. Broadcast TV is mostly for branding anyway, and so the purview of the biggest boys.Is it more difficult to reach the "right" people or is it more difficult to reach enough people
A to your Q is 'the right people', but for the right price. It's easy to reach large numbers, there was/is a fallacy among novice marketers that the more people you reach, the better—but the result is nearly always excessive server costs from all the traffic, with very little of it turning into profitable action… so a money loser.
Better to reach 1,000 people who are your main target audience, than a million who are not. Problem is that those with such demographic segmentation charge thru the nose to use it, so again it's a RoI question.