Chris_O's answer seems to indicate the "managed" hosting product is generally poorly managed.
But isn't the point of managed hosting to get exactly what you want by paying a professional to do the labor? We can't assume VPS hosting professionals are generally incompetent and/or unwilling to offer anything but Cpanel.
Of course a paid professional can do the job better than a newbie, ceteris paribus. But where are you shopping for managed hosting? How much are you willing to pay? How honest is the sysadmin? Etc.
So managed hosting should be "better for performance" if the sysadmin knows his/her craft and you know what to ask for.
I have no affiliation with this company (random example) but does this sound like they're asking you to use Cpanel? From Atlantic.net's "Managed Hosting" page:
"You tell us your vision and goals and
we will work with you to develop a
Dedicated Hosting solution
specifically to meet your needs." "Let our Cloud Engineers help you design, install, manage and monitor a private cloud infrastructure designed specifically for your needs." Etc.
No mention of VPS on that particular page, but they offer it.
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