If any of those games on Epic are also sold in steam, then the (nonsale) price cannot be lower than the steam price because of steam's TOS.

Also the "industry standard" was arbitrarily chosen to match the cut that brick and mortar stores usually operate at... Despite there being very different costs related.

But yes, steam is being just as greedy as all the other big walled gardens. People complain about that rate across the board, not just about steam.