Your reasoning is correct, though you’re missing the scale of the problem.
Enterprise SSDs are being made with higher endurance MLC cells, and can tolerate very high write-rates. SLC still blows high-endurance MLC out of the water, but in most cases the lifetime write-endurance of HE-MLC exceed the expected operational lifetime of a SSD.
These days, endurance is being listed as “Lifetime Writes” on spec-sheets.
As an example of this, the Seagate 600 Pro SSD line has a listing of this, roughly:
Model Endurance
100GB 220TB
200GB 520TB
400GB 1080TB
Given a 5 year operational life, to reach the listed endurance for that 100GB drive, you need to write 123GB to that drive per day. That may be too little for you, which is why there are even higher endurance drives on the market. Stec, OEM provider for certain top-tier vendors, has drives listed for “10x full-drive writes for 5 years”. These are all eMLC device.
Yes, R5 does incur a write amplification. However, it doesn’t matter under most use-cases.
There is another issue here, as well. SSDs can take writes (and reads) so fast that the I/O bottleneck moves to the RAID controller. This was already the case with spinning metal drives, but is put into stark light when SSDs are involved. Parity computation is expensive, and you’ll be hard pressed to get your I/O performance out of a R5 LUN created with SSDs.