No doubt the lobby is extremely influential, and because of that Israel often gets away with actions that are against US interests as perceived by “realist” analysts. But the “realist” side is only faction of the US policy establishment, there is also the neocon-military complex that is extremely influential, and in their view Israel serves a very useful purpose. Historically, the Mideast and the Arab world harboured forces that were not under the control of US policy makers – Arab nationalist in the past and now Iran and Shia movements that support it.
Israel is a great regional military power that can disrupt these uncontrolled elements, and that would be an important asset if it came to a military confrontation. Israel has demonstrated its capacities repeatedly, for example by striking nuclear facilities in Syria (and I believe in Iraq), and assassinating Iranian nuclear scientists. It is no accident that there is close cooperation between the US and Israeli military and intelligence apparatuses. I doubt that these close links are simply the result of the US pro-Israel lobby’s influence, would note that such long-standing close relations are hard to break. There is a reason Israel has been called a “US aircraft carrier” in the Mideast.
It could be argued that with the demise of Arab nationalism and Egypt, Saudi Arabia, and other Gulf states abandoning their traditional hostility to Israel and forming closer ties the West, there is less need for reliance on Israeli military prowess. But the destabilisation of the region along with the rise of Iran and the Shia movements, as well as the renewed presence of Russian military and diplomatic influence in the region has perhaps more than made up for the change of heart of Egypt, the Saudis et al.
I would agree with @Donald that both the lobby and “national security” considerations shape US Mideast policy.