Yeah, exactly. Marth's hitboxes are effective in Melee because what other characters gain from hitboxes that have extended time, Marth has extended space. Being able to threaten from a distance is effectively the same as being able to throw out a long hitbox that stays in their way. The big difference is Marth has really weird commitment levels. Poorly spaced aerials require FULL commitment because if you don't hit them, you have a lot of lag. Well spaced aerials allow him to throw out almost any aerial and be safe from 90% of counter attacks out of shield. The occasional WD OoS utilt from a Doc/Mario or WD OoS dash attack from Sheik may land, but they all rely on you fairing early because if you late fair, you can (as far as I know) ALWAYS get off a utilt or at the VERY least get your shield up before anything remotely threatening happens.
Even if Marth does an empty hop with no plan of doing any aerial at all, what can they do? The fastest thing they can do OoS towards you is a WD, and you can pretty easily react to that and fair them. They can roll away while you wait, but that's just giving up huge amounts of space with virtually no risk on Marth's part. Falcon is one of the few (only?) characters that can actually surprise a Marth floating in his SH with a quick move (nair/uair) except, obviously, another Marth. Everyone else is mostly stuck with the choice of stay shielded or GTFO. And Marth has plenty of "**** you" responses to people who do try and run from him. Whether it's a simple land and run up grab, dash attack, or WD forward to continue pressure, any time anyone shields against a Marth SH in tipper range it's disastrous for them the majority of the time.
As for when rising fair (or SHDF specifically) is useful, I think it's fine if you can hit-confirm or if you are the one on the defensive. If I am shielding vs. a fast ground character, I'd often opt for fade away double fairs over WD back because it's very safe and there's always the chance you'll catch them chasing you. I think using it as any sort of aggressive pressure (even when they're not in shield) is a tactic that's falling by the wayside because people are simply better at observing Marth and punishing his laggy *** aerials when they are used too far off the ground.