I used the app for many years, but stopped doing so due to 3 short-comings a while ago:
(1) It is not possible to migrate backup data from one cloud provider to another, which I might want to be able to do in the case of pricing or service changes (B2/Amazon Drive), new providers (Wasabi), lack of reliability, etc. If I want to retain my historical backups/archives, I am locked into the originally chosen cloud space vendor forever. This for me was the main show-stopper; the company behind Arq has stated multiple times over the last years (both on Twitter and via eMail) that this lock-in is a known fact and provider-migration is not supported.
(2) Arq is very destination centric, rather than source centric. One cannot create one file selection for backups and then back this selection up to multiple destinations, rather one needs to manually recreate the selection for every destination, and keep it in sync manually.
(3) The Arq Backup agent requires a significant amount of CPU cycles. A well-equipped 2015 MBP became unusable every time Arq was performing a backup, which made Arq unsuitable for continuous backups.