one area I see you are confused in is Data Bridge replacing products like Security Assist. What that means is that Security Assist is no longer offered as a stand alone product, but is built into Data Bridge. In Other words, you can no longer purchase Security Assist 2.0 on its own. To purchase the Security Assist functionality, you need to purchase Data Bridge.
Data Bridge is a package of what used to be stand alone extensions:
--CSS Button Styler
--CSS Form Builder
--Digital File Pro
--Dynamic Web Charts
--Validation Tooltips for Spry
and Design Extender is also a package of what used to be stand alone extensions:
-- CSS Sculptor
-- CSS Menu Writer
-- Framework Builder
-- PowerCMS Builder
-- Pro Maps for Google
-- Site Import
-- Site Sculptor
-- Social Media Toolkit
Now, you ask about Power CMS replacing HTML Editor, this is not the case.
Power CMS is a tool that uses HTML editor, it creates a full CMS System, and part of that CMS System uses HTML Editor.
you can still use HTML Editor on its own though.
AS for MySQLI, we are in a transition period right now.
the original MySQL extensions where built on the groundwork of the Server Behaviors that where natively available in DW.
The MySQLi server behaviors is a recreation of this groundwork using the MySQLi library, using that ground work we will be upgrading the other extensions to also use MySQLi. we have already upgraded eCart for MySQLi, and plan to upgrade Data Bridge for MySQLi in the first quarter of 2015. then we will upgrade Design Extender.
It's not that the Authentication in MySQLi server behaviors replaces Security Assist, it is that it is a separate tool based on the native User Authentication tool that was available in DW.