well up b offers a few things that those other attacks dont. the fact that it cant knock them down means that they cant double stick DI tech it into the ground, like you might try to do to survive a falcon punch. also, the angle that it sends at can be deadly if you hit your opponent near the edge, ESPECIALLY if they are a fastfaller or have a very linear recovery (for example, ike). these two things are not offered by fsmash, as fsmash can be double stick DI teched at very high percents (percents that would mean guaranteed kills with up b) and even if they do not tech it in this manor, they can easily just DI it up to survive, as fsmash doesnt have that much power. very few people use the double stick DI tech i speak of (if you are confused, go to youtube, search it, and watch magus' video), but against people who do use it, you find it very hard to kills in the ways that you are used to. simple fsmashes and dsmashes will be relatively useless (at least in terms of killing) until percents that are well past kill range, as in, you should have already killed them.
likewise, in an ideal world, you will mix between your options anyways. Dash attack would be one of my recommendations for lower percent tech chases, in conjunction with JCed grabs, as they will both net you a good set up. but when you get into kill range, dash attack will most likely not net you anything. that is where i recommend you mix in up b, as it has superior coverage, speed, and killing power. obviously, up b would be a very poor choice at lower percents. sticking to one method is a very poor method in general, and that is why i think up b is so useful. it lends you an additional option with potential for great reward at kill percents. right there, thats a threat to any opponent who is trying to predict how wolf is going to tech chase them, as increased options and coverage make predicting anything and reacting properly very difficult.
obviously at lower percents there are better options, but the sort of tech chasing im talking about is the kind when theyve just entered kill percent, and one move that can cover almost all of options, cant be teched, cant be DIed, and sends at an extremely difficult angle to recover from is hands down a great kill move. once you get into the 100 % range, that it when this move will shine. if you dont believe me, just try experimenting with it a little bit to see the kills you can gain with it.