Not just that but also to save other sites on the server from a DDOS attack. Spending a few extra bucks per month for dedicated resources is better than making all your sites hosted on a shared VPS go down due to a DOS attack that is targeted towards a single site hosted on a shared server. I run 100+ cloud servers at the moment and I can configure stuffs on any server within 10 secs max. If you want to save administration time, learn more about puppet, chef or ansible. Will save you loads of time. I don't disagree with you but the market I'm in and the clients I deal with are completely different than what you suggest. Peoples who want power, performance, security and reliability can't expect it when they share the resources with several sites. The biggest reward you get when hosting on a dedicated VPS is the peace of mind. Something you don't get on a shared environment and that's worth the extra bucks. There's a difference between riding a Maserati and travelling on a public transportation like Bus even though both gives same amount of mileage with the same fuel.
You are changing the dynamic of the conversation.
The OP noted he is looking to install cPanel to manage his own websites/domains which means much of your points are unfortunately for not in the current context. Coming to your point of having a separate VPS for each clients, that is certainly a good solution especially when you have high priority clients where the utmost security is within their budget.
As to the "peace of mind", a VPS/Cloud VPS is still a 100% shared as far as the host node is concerned.
-CPU - even with pinned CPU cores, other services will still hit your core as the host node balances resources.
-RAM - RAM can be dedicated in the sense that is can all be allocated at boot time of the guest, but almost all virtualization system have some sort of memory sharing and enabled by default.
-HDD - While you can thick provision the space, there is almost no way to dedicated I/O.
-Network - All shared unless they are giving you a dedicated NIC port which next to no cloud/vps provider will do (makes no sense).
All in all, you if you are a good sysadmin working inside an ethical hosting provider you should be sleeping peacefully at night no matter it a VPS or shared web hosting. That said, no matter how you host your websites as long as you have good backup solution you should be sleeping well no matter what knowing you can easily recover in the event there is a failure.
In the end, each to their own. Everyone has different ideas on how to properly manage a deployment and it will always depend on the clients budget.
