It's quite important to note that, in most cases, defense and offense are not really specific to a move (as in no single move makes a character or game defensive or aggressive), but are rather results of a character's kit. It's very rare, for a custom move, or several custom moves at once, to change a character's over-all playstyle so drastically (Palutena being an outlier, due to Lightweight and Superspeed) as to reclassify their playstyle from one lean to another. It's important to market customs as what they are: both an additional layer to the meta-game knowledge of matchups and options, and an in-match way of tweaking characters to suit scenarios better.
There's no guarantee they'd make the game faster, or more aggressive, on the whole. But there is evidence suggesting that they make many characters more versatile or viable, and in a lot of cases, in ways these characters really need in order to keep up. There's some room for preference - to my knowledge none of these is objectively a pure upgrade, though many are subjectively vast improvements (such as Power Vision) when used skillfully and in appropriate doses. What that tends to indicate, especially with a lot of top picks wanting 0-1 customs in their arsenal, is that these moves do improve balance over-all, and offer more dynamic play.
The big hope for Online Tournament Mode is that there will be some way... ANY way to ensure (short of invitational and honor-bound player pools) that Custom Equipment is off while Custom Moves are on. While they're bound to the same system, there is always potential for a player to subtly (and unless they tweak things, untraceably) cheat on any online customs event.