Earlier quoted context omitted.
DCT is not an algorithm at all, it’s a mathematical transform. It doesn’t have a compression ratio.
> DCT compression, also known as block compression, compresses data in sets of discrete DCT blocks.[3] DCT blocks sizes including 8x8 pixels for the standard DCT, and varied integer DCT sizes between 4x4 and 32x32 pixels.[1][4] The DCT has a strong energy compaction property,[5][6] capable of achieving high quality at high data compression ratios.[7][8] However, blocky compression artifacts can appear when heavy DCT…
Therefore, it has no compression ratio, and it doesn’t make sense to compare it to other algorithms.