??? I thought they were snake folk? Why the change this makes no sense?

This is the version D&D has used for Lamias since 1e. IIRC, there is some medieval precedence for this version. Up until 3e there were referred to as 'common' lamias and the serpent version were 'noble' lamias, but I assume in 5e the decided to just stick with the leonine version to keep them distinct from other snake bodied monsters like Yuan-Ti and Marilith. I do wish they included the snake version too

The change to Corrupting Touch is crazy! If you fail the save, you're Charmed which means you cannot harm the Lamia for an hour. It's CR 4, so if you're using this as a solo monster against level 3s or 4s, a character will be essentially out of the fight with one failed save.

Honestly, I think I prefer the old one. 

Disadvantage to Wisdom saves and skill checks is mechanically so useful. And while Charmed is a great save or suck, it can be more gray to role play, especially when in combat as opposed to a social setting. Pairing the Lamia with others with Wisdom save spells can be game ending.

It does seem crazy, but it is also balanced by having low HP. PC's can easily end it in a round or two, which means it has limited opportunity to actually charm anyone. So it actually really relies on this mechanic in order to be a challenging enemy.

If things do go poorly, rather than TPK, the Lamia might end combat by charming all the targets then sending them away. An hour later, the PC's regain their senses finding themselves long gone from the lair, perhaps missing their gold or other items. Do they cut their losses, or try again? 

I personally wouldn't change it, but if you did want to make it easier: 

• It is effectively the Charm Person spell, so you may choose to follow those rules for how it operates in combat - i.e., in combat players have advantage on the saving throw and it ends if the Lamia does anything harmful to it.

• Alternatively, you might rule that in a combat situation the target can make the save again at the end of its turn.

in the extended FR lore, Lamia nobles have serpentine bodies, implying the default one in the manual is a lower class.