I understand the Iranian decision though. Iran dealt with severe sanctions. Iranian Migs and Sukhois were not bought by Iran, they were confiscated by Iran when Iraqi pilots fled to Iran during Desert Storm. Russia was still scared of sanctions back then. Iran has no supplier of aircraft except itself, and its maximum effort could only make F-5 style planes and keep F-14s flying. It can't compete with heavy 4.5 gens and 5th gens.US/Israel will give Iran an ultimatum. To give up it's nuclear program or face destruction.
If Iran refuses, then I very much see the possibility of US joining this war. Israel has degraded Iran enough that it should be easy.
Iran has no Air Force. Their AD are being picked apart from both within by infiltrated forces and by SEAD/DEAD ops. It's only a matter of time before IAF achieve Air Supremacy over Iran. Right now they have Air Superiority on the western and some central parts of Iran.
Iran can't win this war because they never focused on improving the most important thing that matters in modern military, their Air Force. All they cared about were ballistic missiles. They also viewed their AD as more important than their Air Force.
I'll give Pakistan credit for not falling into this same mistake and constantly working to improve their Air Power.
Iran is rightfully paying the price for their negligent military moves. They can inflict damage to Israel but will still lose.
There is no way they could've competed against 100+ F-15s and F-35s. If Israel was only using F-16s it would be a different story but F-15s and F-35s are too much. If it did not invest in missiles but instead, say, invested that money into buying 36 Su-30s off the black market, it would just be doing 0 damage and getting most of its air force shot down, like what happened to Saddam.
Ukraine and North Korea got away with a poor air force because they neighbor their opponents. Iran doesn't anymore, so they can't hit back with ground forces under cover. They were screwed when they gave up their proxies. If Iran still had Hezbollah, they could launch ATGM, FPV and mortar attacks into northern Israel but since Iran abandoned them, Hezbollah is sitting it out.