NEED HELP! Full storage on ipad! Does iCloud storage really not help?

Phone storage & iCloud storage. 

After readying a couple threads here about low storage issues. I think I realized that I’ve been  paying for extra iCloud storage for nothing after all. 

I originally bought more data storage for myself because my current iPad and iPhone have the smallest amount of device storage on them compared to  previous apple products.

 I noticed my iPad and iPhone filling up, so i eventually bought iCloud storage.

 But if I’m not mistaken, I just found out that

- iCloud storage isn’t a solution for low data thats physically stored within the device. 

-A actual solution would be: finding out whats being stored on device, then by evaluating whats most important & what could be deleted. 

If the above points are true, then I don’t understand what’s eaten up all my space on my devices? When i view my storage data on my phone. By clicking: Settings/General/ iPad Storage.

The iPad it shows in this order:  photos, applications, iPad OS, Books. 

Why wouldn’t extra purchased iCloud storage help me in this situation? iPhoto i thought for sure, every photo/video is synced to the cloud (therefore within iCloud storage?). 

Same with apps are stored in the iCloud? 

I noticed that the majority of my applications are not even stored on my iPad anymore. When i click on these apps, they have a little cloud next to them, (assuming they’re in the cloud) & when i click on  any of these apps, it shows the application redownloads.

If most of my apps seem to be on the iCloud then how can they be the 2nd most consuming data problem right behind iPhoto? HELP