I've just replaced the hard drive (320gb) on my netbook (Ubuntu Mate) with a 1TB ssd. Yes, loading from drive is quicker but overall it doesn't make much difference in speed, as most computing processes run from RAM.
So, in speed SSDs are overrated for their price, which is about 5 times more than a spinning disk in £/GB. Ie they are not 5 times better.
"I bought a new car but it hasn't made my bike any faster."
But it has made my computer faster!
Well a faster car might give you time for more
CAKE when you drive to the start of the ride...
I'd expect a substantial speedup of reads - especially random reads - with an SSD compared to spinning rust, and if my computer was slow due to poor storage throughput, that's what I'd upgrade to speed it up. If it was slow at some CPU/memory/network-bound operation, I wouldn't expect any improvement. If someone's given you the impression that SSDs are a magic box of 'more speed' you can add to your computer, then that's a misleading oversimplification - it doesn't mean that SSDs are in general overrated, they're still a step-change in performance compared to magnetic disks, and usually more reliable.
(FWIW, I find that Windows desktop systems seem to spend more time thrashing disk than Linux ones do, which means more IO-bound tasks that can potentially be speeded up with faster storage.)