In order for Steem to be a security the interest has to come from the effort of others. The Howie test is supposed to be what determines if something is or isn't a security.

See here:

The SEC sued the defendants over these transactions, claiming that they broke the law by not filing a securities registration statement. The Supreme Court, in issuing its decision finding that the defendants' leaseback agreement is a form of security, developed a landmark test for determining whether certain transactions are investment contracts (and thus subject to securities registration requirements). Under the Howey Test, a transaction is an investment contract if:

• It is an investment of money
• There is an expectation of profits from the investment
• The investment of money is in a common enterprise
• Any profit comes from the efforts of a promoter or third party

Common Enterprise defined:

In the context of an investment contract, a “common enterprise” is defined as an enterprise in which the fortunes of the investor are interwoven with and dependent upon the efforts and success of those offering or selling the investment or of third parties.

I don't know if Steem Power is a security but because it's an algorithm behind it rather than efforts of promoters or any specific employees it likely isn't one. The profit if it comes from an algorithm is guaranteed only by math. The other question is what would be the common enterprise? Steemit Inc?

If and only if Bitconnect really had a bot then they could not be a security but we never saw the bot which means it very well could have been one guy with a laptop.