Yes, SteemP is pegged to Steem and simply sending Steem to Steem-engine doesnt do anything to the price of Steem.
Steem-engine tokens on the other hand are nothing more then Steem alt coins.

Saying that Steem engine is reducing the price of Steem is true to a degree, depending on which token youre talking about. Tokens that are essentially bots whose value comes from being able to buy votes on Steem are indeed devaluing steem.