For over a decade I ran a small scale dedicated and virtual hosting business (hundreds of machines) and the sort of setup you describe works very well. Software RAID across 2 devices, redundant power supplies, backups. We never had a significant data loss event that I recall (significant = beyond user accidentally removing files).

For quite a while we ran single power supplies because they were pretty high quality, but then Supermicro went through a ~6 month period where basically every power supply in machines we got during that time failed within a year, and replacements were hard to come by (because of high demand, because of failures), and we switched to redundant. This was all cost savings trade-offs. When running single power supplies, we had in-rack Auto Transfer Switches, so that the single power supplies could survive A or B side power failure.

But, and this is important, we were monitoring the systems for drive failures and replacing them within 24 hours. Ditto for power supplies. If you don't monitor your hardware for failure, redundancy doesn't mean anything.