A couple of reasons I can think of why it's not nearly as good:
You can do the asdi down so that it bounces you on the ground instead of up in the air. It works to a pretty high percent (I don't know what it is, but I feel like it's at least past 50% for most characters). CF's forces them into the air no matter what at a much lower percent.
when CF gets a stomp he either gets a guaranteed kill if it's at the right percent/stage position or a very high chance of ****. When marth gets the dair its not necessarily any better than just having grabbed them again.
At some highish percents the tipper hit probably sets up for some finisher guaranteed, but saying it's like CF's stomp techchase is pretty ridiculous imo. Does anyone know percents where tipper dair will guarantee a strong finisher?
the stomp techchase is also really good in some situations because he can do it super low to the ground and cover other tech options if he has a little bit of assistance (i.e. the edge of the stage limiting techrolls). I think Marth's is too laggy to do this with since you can't do the dair late if you want the tipper hit, right? And if you don't get the tipper hit the cc/ground asdi works to an even higher percent. Sometimes you get straight up cc punished for doing it.
The CF-ish thing Marth can do with it is like space a sh in front of their tech like you're trying to hit their tech in place or something and DI backwards a bit and dair their techroll back. that's pretty cool I guess.
About downsmash, its pretty **** and I feel like marth players should eventually figure out the spacing for the tipper/some reliable traps for it, such as catching their techroll back with the backwards tipper hit. It's easily the strongest finisher Marth has. Sometimes I feel like you can cc dsmash some spaced moves that you can't cc grab, but this could just be me being a Luigi player too used to spamming cc dsmash.
About shield breaker, the main uses I know of that are useful are finishing aerial combos where reverse up b/spike/inside fair won't hit, and jumping out to edgeguard firefox/firebird charges in weird situations that you can't get there to reverse up b in time and don't want to risk doing a tipped fair instead of an inside one. Aggressive shield breaker edgeguards are pretty good vs falcon too imo but you can edgeguard falcon in any way you want as long as you're precise, so that's whatever.
Besides those and edgeguarding I'm not sure how the move could have a lot of applications since it's not particularly strong or fast, and it's laggier than Marth's other options in almost any situation. (and it's my favorite marth move kind of so I use it whenever possible.)