If Israel thought that J-Street had greater pull, then there would be a higher diplomatic representative at the event. As you point out, to J-Street supporters, Israel is just not that important. By comparison, Israel is a front and center issue for AIPAC supporters. To them, there is a single issue, the support and safety of the Jewish state. This is a much different stand, akin to a football supporter saying "I like my team" as in "I like to breathe", whereas some regular joe says, "I like football, when nothing better is around." As for the core of American Jewry, I believe it falls more into the category of "We believe in Israel and support it as a free and independent state able to live in security" I've been to many synagogues over the years, and the core belief of both the leadership and congregations fall under the banner of pro-Israel Zionism. The question for a Zionist is not peace or war, but do you support Israel's right to live in peace and security.
Biden says cannot say yet whether he will mount White House run (Reuters)
from the article: Israel envoy Michael Oren rejects J Street invite