Israel's Supreme Court. Completely out of line, but What do you Expect?

Jonathan Sumption (former uk supreme Justice) pointed out in his Reith Lectures that the courts fill political vacuums (and usually in way much less satisfying than if they are filled politically). 

I think that by creating a pure unicameral system, Israel left a gap that has been filled by the Court. The question is how can this gap be realistically filled, hopefully in a Madison-esqu way. Direct election of the head of government, did not solve this problem, perhaps because it didn't resolve the problem of checks and balances. Westminster systems (like the UK and Canada) that have diminished the strength of their upper house have seen a similar issue. 

Going forward, how can this gap be filled without an unlikely constitutional convention like event or aggressive FDR-like tactics? The vacuum in the separation of powers is real. Maybe it was masked by much of Israel's early history being dominated by one side. 

However as the tide turned to the Right in power and influence, the weakness of the unicameral system has been revealed. I wonder if the answer is in devolving power somehow.