DI in Smash 64 is more difficult to do than DI in Melée. The L-cancel in Melée is a nerfed Z-cancel; because all of your landing lag in 64 is canceled, you have even less time than in Melée to input your next move for perfect play. These things do not make 64 a less technical game than Melée; they make it a
more technical game. They require at least equal, if not greater, precision for consistent execution (for those two aspects of the game, anyway).
In a larger sense, I would guess that Melée players' dismissal of 64 as being "not as technical" as Melée is more an indication that they think that 64 offers fewer interesting scenarios and options than Melée. They're not concerned about technical execution as they are about technical depth. It must be admitted that 64 doesn't have as many movement options as are available in Melée; there's no airdodgeing, and subsequently no wavedash. There's only one kind of shield, not three. The character roster is smaller. The number of competitive stages is smaller. These things reduce the options players have; they reduce the game's possibility space. And I would venture that when a Melée player says that 64 "isn't technical," they're thinking of these limitations, and concluding that they make 64 a less expressive, less creative game to play. Because you don't have as many options, you can't be as free-flowing with your gameplay.
I think this is a short-sighted mindset. The basis of the argument I'm about to outline has been much more rigorously and zealously developed by Oulipo (official site:
http://oulipo.net/ Wikipedia:
https://en.wikipedia.org/wiki/Oulipo). The fundamental idea is that "constraints are liberating." Having fewer options, in many cases, forces you to be more creative. Because you can't spam as much tech skill to move around the stage or refresh your ledge invincibility, you have to think in ways you're not used to, and come up with ideas that operate on different premises. You need to be better at the things you can do, because there's no getting around them, or compensating for a bad gameplan with faster inputs. 64 is great for this. You don't have as many movement options, so your movement has to be more deliberate and precise. Not as many things are punishable out-of-sheild, so you need to rely on it less. The roster is smaller, so matchup knowledge is more important and easier to gain (on account of the fact that you don't have to spread yourself so thin to play every character and you're more likely to meet someone who plays any given character).
Because 64 isn't as fast as Melée and doesn't make you press as many buttons, that may give the impression that it's "less technical" than Melée, but that just makes each individual button-press more important. The execution cap is still high; as I mentioned earlier, your DI and post-cancel inputs have to be more on point in 64 than they do in Melée, and shield breaks with Mario, Ness, Yoshi, and Fox are hard enough to do that you don't see them often in tournament play, even though they're guaranteed. But where 64 lacks in total speed, it forces you instead to be more thoughtful and deliberate.
The technique required in 64 isn't so much in pressing buttons fast, it's in figuring out how to do excactly what you want with a limited set of options. It's hard, but some people make it look easy.
But good luck getting a player who's walking over to the Gamecube setup to listen long enough to convey that. You'll probably have better luck just getting them to sit down for a round ("Come on, just one game") and explaining 64 tech and metagame while you're playing. If they're not interested, you can't make them listen.
