It's a bit of a trade-off. An existing browser for example will likely just add the format, effectively creating more attack surface, yes. A new product however can choose to only implement the simpler one (and if no features of the more complex one are needed, will likely want to do so for a multitude of reasons).
Over time, the old format may potentially be removed if it falls in disfavor, or at least only be accepted in more and more restricted contexts, but this works better in closed systems of course. I just finished excising a complex format in favor of a much simpler one, and since it was internal to the organization cutting out the old one did not cause anyone problems. For browsers, I don't know. Deprecating Java Applets and Flash seems to have worked, but those are maybe "heavier" examples than SVG.
As for comparison to existing vector formats, I don't have the necessary domain knowledge there.
Over time, the old format may potentially be removed if it falls in disfavor, or at least only be accepted in more and more restricted contexts, but this works better in closed systems of course. I just finished excising a complex format in favor of a much simpler one, and since it was internal to the organization cutting out the old one did not cause anyone problems. For browsers, I don't know. Deprecating Java Applets and Flash seems to have worked, but those are maybe "heavier" examples than SVG.
As for comparison to existing vector formats, I don't have the necessary domain knowledge there.