@Gary.D
Cloud storage means you put your data on another company's hard drive. You have full control to your own data, you access it when you want, you upload, download, move, delete, whatever you want in your own way, you can create folders to make your filing options suit your needs. It is your data, yours alone.
But you have no control over their hard drives, their machines, their business and their staff.
A business could fail and goes bust (unlikely with big cheese companies like Google, Microsoft, Adobe, etc., but can happen with small companies). There is the possibility of a hostile takeover, where one company would take over the other company. They do have to maintenance their hard drives and computers, thus would move your data over to another hard drive while they upgrade their outdated hard drives, then move your data to the new drives. Therefore they are making an effort to keep their machines in good working order, which imply that their machines can fail if they don't keep a good maintenance. They have no control over outside matters like freak weather or terrorists blowing up their buildings. They will have fire fighting systems in place (ie: Smoke alarms, sparklers. staff who are quick to phone the fire services, etc.,) but nevertheless, like with every other companies, they too could find the building go up in smoke. They like us, are trying their best to keep out hackers and viruses, and they like us, could find their computers hacked into. There is always this rare case that one member of the staff do something stupid. (Wasn't there a story where this Twitter staff got fired or laid off, so in revenge he decided to shut down Trump's Twitter account?)
The better option is to accept that both of them, your own portable external HDD and the cloud storage, each have their own pros and cons, so there is nothing to stop you opt for both options at same time. You can always back up to your own HDD and also back up to cloud storage. That way, if one goes wrong, you still have the other back up.
Plus: In a few years time, you can always upgrading your external HDD to a new one, transfer (or make a fresh back up) to the new one. Beside, that is what they would do at cloud storage anyway, like I said, transfer your data over to another hard drive, while they upgrade any aging hard drives.
Also cloud storage companies sometimes update their software, which means that they may sometimes change the options. For example, you want to back up data to the cloud, and leave it there. Delete from computer, but it stays on cloud. Then few years later, they updated their software to a new system, where the files will be deleted if inactive for some time. Or they change the storage space allowance, for example you upload to a free 5GB storage space, but few years alter, they decided to change it to a free 2GB storage space, and for the 5GB option, you pay for it. It is their business to run and therefore they do that they think is best for their business.
On your own external HDD, you are the master of your own options. You just create a folder and call it (say for example)
Archives, then you transfer your data to it and leave it alone for years to come.