I found this while doing some browsing, it's not an accurate take of the numbers, but I wager its pretty close.
Here's some data from the most recent redump dats. This counts every version and regional variant of all game discs currently dumped for these systems. Please note that these sets are still incomplete (especially PS3), so these numbers are expected to grow. The sets have already grown quite a bit since I first did these calculations about a year ago.
Also keep in mind that I've just added the sizes of all the uncompressed ISOs; using various compression methods, you can probably save >50% at least for PS1 and PS2.
PS1:
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Total set size: 3.722 TB (3811.252 GB)
Total dumps: 8502
Average size per dump: 0.448 GB
PS2:
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Total set size: 17.741 TB (18167.278 GB)
Total dumps: 7738
Average size per dump: 2.348 GB
PS3:
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Total set size: 16.818 TB (17221.684 GB)
Total dumps: 1877
Average size per dump: 9.175 GB