Would the reading speed of those SD cards be as fast as the reading speed of Blurays?

Disc speeds are notoriously slow. PS vs N64, Cartridge based systems were instant where as discs had to be loaded into a ram space/buffer and had terrible load times. The difference back then was that disc's had a boatload more storage where cartridges were very expensive to get any significant capacity. That's still kind of true today, but at scale not nearly as much as it used to be, and max capacity of sd cards are WAY bigger than discs overall.

6x Bluray drives (which is what is in the PS4 for example) read at about 27MB/s. I don't know what speed the PS5 is, but bluray supports up to 72MB/s as a standard and has it's highest capacity at ~100/128 GB.

Meanwhile... You can hop on amazon and buy 200MB/s sd cards no problem. I've seen them as "fast" as 300 MB/s, and as high capacity as 1TB. So easily 3x more bandwidth, and significantly more capacity. Usually costs more though. Some weird side-benefits though... You can actually update the game that lives on the card. You can leave some assets on the card that get called less often when you install to SSD to save space on internal storage. Or if you're live loading assets from the sd card to an internal SSD, any load times will be significantly faster. You CANNOT do these things on spinning disc, it's too slow.

The real difference here is latency though. A disc has to spin... You have a physical laser head that has to seek to a particular sector. That's slow as hell and at the density of tracks that you have to do on BD-XL disks, you can actually overshoot tracks if they're laid out poorly which increases the delay of getting the data. SD cards don't care at all, everything is nearly instantly responsive.

So yes, sd cards are significantly faster than bluray discs in a number of ways.

Edit: Minor edit to make it more clear.