Its not about the transfer speeds, its about seek latency. HDDs seek on the order of 5-20ms; SSDs are roughly 10-1000x faster in seeks.
So if you're reading and writing sequentially, sure, a 2-3 drive RAID 0 could match the SSD. But for database apps? No way. SSDs maintain ~500MB/s on random workloads on fragmented drives. An HDD would be lucky to hit 10MB/s in such a scenario.