Takes a lot to get a lurker and occassional visitor like me posting. While I think I can see what DE is thinking, I must say their phrasing is very worrying.
There were/are memes that DE acts as if it doesn't know or isn't aware of how their game works, and the phrasing in this post (sad to say) goes some way into proving the point.
To adress point 1),
-It is the Combo Multiplier that amplifies damage.
-The Xoris' Combo Duration adds a lot of convenience.
-Riven mods, with the disposition for equipped melee weapon affect some warframe abilities.
To address point 2),