No. Consumer grade cloud backup is not an effective solution. In fact no single solution will protect your data, you must mix it up a bit.
To give you a good answer I would have to know about your habits, usage patterns, and a lot of other details, but here is my best guess based on an average home/small business owner I'm usually working with.
So, to backup, or to be exact archiving.
It's a very complex question and you should decide how much you can afford to lose. Providing a 99,9% data security is a VERY expensive affair (think redundant geographically scattered storage with no single point of failure). Data can get lost in many more ways than you think, not just ransomware. For example DVD or BR-D will only last a few years, flash drive will be dead in around 7 years, typical hard drive is not usable after 5 years, format may get deprecated, interface may get deprecated, hard drives may make uncorrectable errors (and in fact they do), your backup may be killed by lightning strike, fire, flood, it may get stolen, you could lose your password if you encrypt (and you should)... Just imagine a nightmare scenario where you have NTBackup archive on a failing IDE hard drive - fun.
So a few solutions:
First of all, monitor your filesystem. Ransomware attack will create huge filesystem changes and you will know there is a problem right away.
OPTION 1 - go with M-Disc. 100GB of data is not that much, so you can make two copies of it on 100GB M-Disc BDXL. Put one in a drawer at home, put one in a bank safety deposit box and you are good. For a millennia, they say. Bear in mind you can still lose your data. It's a read only medium so using it on an infected computer is not a problem.
Between archiving use a full size SD Card (say 128GB), flip it's switch to read only for everyday use and to read-write when you backup. Between archiving, use a DVD until you have enough for another M-Disc archive (pay attention to DVD longevity). I'm not affiliated with M-Disc in any way, but I do have a pretty good experience using it.
They also have Dropbox + M-Disc solution on their website, so you can use Dropbox for convenience, and get your archive shipped in.
OPTION 1.1 - Same as above, but using regular Blu-Ray disc. It' cheaper but much more risky. Make sure you re-burn your archive once a year.
OPTION 2 - setup a small (Linux) file server and mount it's storage for convenience, but make sure it is versioning it's backups to a storage not accessible from your client computers (NAS or Cloud or whatever). So if something goes wrong, mounted storage will get encrypted, but you can always go back as the server itself is not infected. Firewall it not to allow remote access as future more advanced ransomware may be able to exploit it by stealing credentials from an infected client. Make sure you always have more than one copy of your data, consider longevity of the media used, and replace hard disks on a first sign of trouble.
OPTION 3 - get a credible IT guy to set up a solution tailored to your needs so you get instant access to your data and (almost) bulletproof archive. I know people come here for DIY solutions, but data protection is a science, not something you can sum up in a single page and I'm 100% sure you can't see all the caveats to your solution.
Whatever you choose there is no "set it up and forget about it" solution, and who ever claims there is, is most likely incompetent.