In today's modern military, would there be any benefit to an enlisted structure similar to that of the past?

Yes I was in the army when they had SPc 7... 8 and 9 had already been done away with... they went to lead follow or get out... it is about cost...

I thought the whole purpose was for the non-combative MOS’s

Stripes

None

The sea services that how you advance it you switch rates you get dropped back to E4

Thank you SGT. Joseph Gunderson.

You can mentor without being "in charge". You can be the best at your mos and not be a leader. You shouldn't have to choose between warrant Officer or NCO.

Back when you had the Specialist Ranks in the senior levels they had Pro Pay which compensated the technicians for their advanced technical skills when they could not be promoted higher. This was resented by the Hard Stripes that a 'non-leader' was getting paid more than they were. Just as you had Specialists (And Techs) that would not make good leaders, many to most of the "Leaders" did not have the mind set to master the technical details. Also the Specialist ranks were effectively killed by the Up or Out mentality that came to run our military.
To bring back the Specialist/Tech ranks would require a fundamental change of both pay and retention. There were individuals that served their entire career in the lower specialist ranks but were VERY good at what they did.

I joined the army in 67. We still had a few career privates. I only knew one personally. What was wrong with that?

Yes, with the need for skilled technicians there needs to be a structure to address that, or we lose them, and lose them fast to the civilian world.