How would they even fight Iran? They don't share a border, and you need an army of at least 500k to even properly man the entire western Iran border(Iran Iraq war was I think 600k on each side when there were actual offensives in the mid 80s, and 200k each side when it was just attrition war).

The only way Israel can have a proper war with Iran is by attacking Hesbollah, but thats a whole different topic.