Quite a few misconceptions in here.
First of all, if you're not multiple in today's game, you're slackin'.
3-4, 4-3, 3-3-5, 4-2-5, blah blah blah. Fvck all that.
Those numbers just describe personnel. (i.e. 3-4 = 3DL & 4LB)
What really matters is WHERE you line these guys up and are they able to execute what you're asking them to do.
You need the ability to move in and out of different fronts depending on what the offense is trying to do to you. (FYI - the 3-4 gives you this flexibility more so than any other defense)
I personally run a 3-4, but versus spread teams we remove the Sam OLB and put a Nickel out there. (so is it technically a 3-3-5?)
If we get a team that runs double TE's or heavier sets, we remove the Nickel and put a Sam OLB in the game. (bigger body)
On passing downs we generally slide our 3-4 into a 4 front.
On running downs we play a lot of 3-4 Tite Front to stop interior runs.
Versus Wing-T or Double TE sets we play a 5 front.
See what I'm getting at?
It's all about situations, formations, the objective you're trying to accomplish and WHERE you're lining guys up. Defenses in college football today are stopping the run with only 3 guys on the line-of-scrimmage...but because of the way they're lined-up, it forces all interior runs to BOUNCE where next level defenders clean everything up.
We don't have this level of imagination and implication on defense. We generally just line-up in our "pEnEtRaTiNg 4-3" regardless of what offenses are trying to do. We let the chips fall where they may. And they usually fall somewhere around the mark of 500 yards of offense. Diaz already thinks he's a guru, which is why we've never seen anything different being implemented during his tenure here. He could never bring himself to adopt anything from the rest of the college football world.
I want yall to think about this for a second...
When you're truly multiple, you're never living in ONE THING all game. You have certain fronts/coverages that you like versus certain offenses, or on certain downs/distances, but you're not LIVING in any one thing all game. SO YOU RECRUIT ACCORDINGLY.
Yes you need a good NT to run the 3-4, but if you're not LIVING IN IT then you can recruit a huge body like Jon Ford to play it. You sign him to do nothing more than play the NT when you run your 3-4 Tite front, and a few snaps at 1-technique when you're in a 4-3. Then you have guys like Taylor and JHH to play the DE spots in the 3-4 front with a Nik Bonitto at the Rush OLB spot. When you slide to a 4-3 or 4-2-5 on passing downs then you move Taylor and JHH to the DT spot, move Bonitto down to weak/rush DE, sub another DE to the other side...BAM! You're in a 4-2-5 with an athletic front.
If we're doing this on the HS level then there's no reason we can't do it at Miami. I don't get to choose the kids for my scheme, I have to work with what I get. I imagine it only gets easier when you can specifically recruit what you want/need.
At the end of the day you have to be multiple. You can't just line-up in a penetrating 4-3 all game and run upfield. It's not 2001 anymore. Offenses are way too good and way too multiple today.