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Nothing inherently wrong with it and it of course depends on your storage needs. Online services are so mature now that I don't really hesitate on storing data in someone's data centre now, though, so I can't quite imagine having to plug a hard drive in.......
With that said, if you aren't already, you should periodically make sure those old drives still work. No point in having backups if you can't backup from them!
Apologies if this is one of those annoying questions but I noticed a comment a while back "not time machine".
I have iCloud backing up my phone and my email, documents and work photos from my mac book.
I also backup (periodically) to a hard drive that has Time Machine and some other storage folders. I archive (mothball) the time machine drives about every two-ish years and start a fresh one. This does waste space but it means that there are multiple copies data across the drives. I've never managed to copy the backup files so each new drive starts completely fresh.
I travel a lot and most of my work only exists digitally so a reliable backup is essential.
This has worked for me so far, please feel free to tell me what I'm doing wrong...