I totally agree about m2k. It's frustrated me as a fanboy for so long.
What do you mean by a solid Marth vs a modern Marth? Examples would be cool.
Okay so the way I try to play Marth is a combination of old and new school. They each have very important characteristics they emphasize individually that hurt them overall but can still take them pretty far. I just try to take the good from both and trim the fat.
Old school realllly likes outspacing things. I played with an older player a couple weeks ago, and he was the best Marth main in NC(he may still be now but that doesn't count for much atm like it did back then lol). He made JAB look like a good move, which totally blew my mind. He didn't even use it much. He would just be putting up really weird walls and then if he saw them come in or he suspected they'd come in he'd throw in a jab. It usually hit. This screwed with Twitch(as I was watching the two of them play) and made him respect Marth that much more than if he(Peter, the Marth) were just DD'ing. I mean all he really did was hit someone with a tippered 2-3% move, but it changes things mentally(wait longer to approach, respect walls more, which means you can go in safely for example), which is a less prominent gameplay element that most don't seem to dabble in anymore(you could also call this mindgames or conditioning sort of if you wanted but I don't think either of those are quite right for this for some reason).
PS, walking is OP. Marth has a fast walk that allows him to still utilize all of his options and big moves while being in control of his character and moving his big hitboxes around(theoretically they're always out which is why we space and yeah Marth's big on threatening....I should write about that). Basically, when you run you have fewer options but the goal is/was probably to give up some for the surprise element of Marth's speed or just the contrast from walking in general.
New school wanted to trim the fat, but they ended up trimming too much I feel. So much DD'ing and running and grabbing that sometimes I think people forget that Marth even has moves like Ftilt lol. Still, the maximized efficiency pushed Marth's game in terms of punishment should he get that first hit. Combos, edgeguards, juggles sort of, technical precision....that type of stuff became huge for Marth and it paid off when M2K was also good at getting that first hit/grab by breaking the game down to a 50/50 or better for him when taking in human factors.
The ideal Marth, the solid Marth as I called it last night apparently, is one that takes the understanding of creative walling(which I suppose I'll explain more of in a sec) and move mixups and threatening with the efficient punishments of the modern metagame. Basically taking a neutral position, winning it in as many ways as realistically possible, and then pushing that advantage as hard as possible. This makes sense when written out but I wonder how many do write it out.....
Creative walling is something of a dead art almost. I'm still not very good at it but I understand its importance. When people complained of Marth's range, it was because Marth's were Fair'ing on reaction or threatening with them with empty SHs, or were beating their low moves/shields with Nair, or were cut off on the ground by jab/ftilt/dtilts, or tried to space anything and ate an Fsmash. Then when they shielded they would get grabbed, OR Marth would sit there(threatening). That's off the point of creative walling though. Walling is all mixups, but ground moves chained together or aerial threatens/moves to ground moves or to movement to ground/aerial moves gets pretty complicated and effective if you do it right. Nair(covers some aerials and approaches) to walk forward dtilt(to cover DD'ing closer or grounded approaches) to WD back jab(to cover lag punishment/going high for the dtilt) to double empty hop to SHFF Fair to start new conditioning/re-establish the threat of Marth's moves. I have never done the sequence of things I just suggested in that order but I would have no problem backing it assuming your opponent is reading and not just looking for a couple things to charge at over and over. The moves you use can be seen as less important than understanding what moves come after that, if that makes sense.
The way I look at walling is like this. If someone has a typical approach, figure it out and stop it. You can play your own way until you figure it out and stop it. From then on, you must recognize whether the opponent will come at you harder if you keep blocking their approaches in hopes to catch you spacing for typical moves or they wait longer to try to get you to overcommit and punish your lag(2nd is much more common these days I'm pretty sure). When I played Chillin, I would be caught offguard by how often Chillin would just rush me even when I sat back and countered his "normal" or typical approaches. I would counter them or act as if I was and then take space so it gets easier all the time. That's how I play. Chillin observed this and began rushing me when I always came in to take space and sometimes a little beforehand and it was very unnerving.
Okay long Marth post over lol. If that's confusing then just ask questions. XD
Though, generally, for most, it's easier to time 5 frames than 3 frames. That's not why I have a Fox secondary, and not Falco, but I think the fact that Falco's shenanigans are easier than Fox's, and the fact that it's easier to be consistent with Falco, does come into play.
Fox gets a 2 frame faster jump squat? Nice he can do moves faster and cover more options!
Wish people thought of that in a good way instead of inherently negative all of the time, but that's a pet peeve of mine and I'm fairly guilty of it too.....
To respond to your actual intent, I think that both characters are VERY demanding technically and require somewhat different skillsets of technical endurance(like Fox DD'ing vs Falco laser'ing, as one of many examples) so comparing their ease of use in terms of wear and tear on the player of said character doesn't accomplish much. The general consensus is Falco is easier to use but I'm not really going along with it, simply because Fox gets some easier situations/followups than Falco which pay off for all the (possibly extra) work Fox may have to execute in order to get the hit in the first place.
They both **** lol.