Well it can be detrimental if you focus on just one move. There might be some situations in which your favorite move wont work, so its good to develop at least a second pet technique. What I would say is if your favorite move is a hand strike than work on a kicking move as your next pet technique, if your favorite move is a kicking technique than work on a hand strike as your next pet technique.
What Im saying is this, its a good idea to focus on a few techniques but not too many. Perhaps one or two hand strikes and one or two kicking techniques or maybe a little more. Having just one technique that you work on might not be a good idea because there might be situations where your technique wont work that well. On the other hand, trying to master too many techniques is also not a good idea because you spread yourself too thin, you become a jack of all trades master of none, so none of your techniques are as effective as if you only focused on a few.
An example of a style that only focuses on a few techniques would be Muai Thai. They mainly focus on the low roundhouse. Aside from that, practitioners work on elbow strikes, knee strikes, clinching and locking, as well as basic punches but they don't try to focus on 100 different things like some styles of Tae Kwon Do do as I've noticed from my experience with the style. So that is what Im saying, its good to have a few techniques but more than one that you really focus on, but not too many because then you're spreading your focus too thin so that it isn't really focus and none of your techniques become all that effective.
So, I tried to spell it out for you but if you still don't see where Im coming from that's not my problem.
Speaking for myself, I came from a system (Parker Kenpo) that has over 100 base techs, not to mention various extensions on those techs. That said, when all is said and done, we have quite a wide array of things to pick from. However, I'd rather see that list cut in half. I mean, you can have a million techs, but if you suck at all of them....well, you should see where I'm going. However, just because I have a few punch defenses that I personally like, doesn't mean that I disregard everything else, punch related. I mean, you could have 5 different people throw the same punch at you and odds are, you're going to end up responding differently, because not everyone punches the same. Hell, I've had a student throw the same attack at me a few times, during a class, while I was teaching, and there have been times, when I've had to adjust, due to slight differences from one attack to the other.
As for Muay Thai only focusing on the low round kick...well....I'm going to disagree with that. That low kick is used quite a bit in Kyokushin, which I now train in, however, much like boxing, that only has a handful of punches, it's the way they're applied to a given situation, that makes the difference. So, while there aren't 100 different punches in MT, there are hundreds of variations, all of which are drilled, over and over. A few weeks ago, during my class, we worked on various defenses against punches, and then moved on to kicks. Some of these were strictly for a sparring setting, while slight variations, made them more SD/street applicable.