Hamas is entrenched underground, so is Hizbolla in Lebanon.
In Syria Hizbolla and Iran are also digging in deep.
These aircraft are NO deterrent

The Germans had more advanced tanks, subs, and fighter planes, but the USA and its allies produced more tanks and subs and aircraft than the Nazis and Japs destroyed while their own stocks became depleted.

A 100 million dollar jet? That's a lot of money when a cruise missile might do the job without risking a pilot. With drones armed with smart munitions that are controlled from a safe distance, there's simply no need to have the shiniest toy on the block.

One F-35 could be replaced by a hundreds or maybe a thousand armed drones. The enemy can put all its defenses against a flight of jets and do a lot of damage, but there's simply no way to defend against a thousand armed drones with pilots at the controls.

A BILLION dollars for 10 aircraft? That money could be better spent. As for the rationale that because of Iran's belligerency the planes are needed, it's time to stop this train right here and now and Israel should simply announce that any attack from Iran or an attack sponsored by Iran will result in the destruction of Tehran's ability to generate electricity or produce clean water. Several million people without water and electricity will force the Islamopaths to deal with the problems at home, assuming the people haven't already tarred and feathered the leadership.

and the size of the airplane needed to carry it?

Drones would be a cheaper and safer option. Then the government could take a third of the money reserved for arms for better social benefits to it‘s citizens.

Without violating Ynetnews policy, why would anyone question Isrial's need for such purchase, considering the current political climate in the middle East.

As a matter of fact, it has been my observation that the same people that would ask why, also justify her enemies.

The F16 is a great plane but its also a G4 plane whilst the F35 is G5 and you have to buy the newest and best on the market if your going to stay ahead of the game.
The production line for the 40 year old F15 design will be closing in the next few years and I imagine that within less than 10 years the F16 line will close with the F35 being the only manned fighter that Lockheed will make.

The IAF has had many kinds of fighters in the past starting with WW2 surplus and the F35 is just the latest acquisition.