They certainly have, but the general idea is to first use stealth jets to bomb defensive systems (including radar observability) to conquer the skies, and then you can fly around somewhat freely. While SAM technology has improved, so have America's observability and stealth bombing capabilities. It will be interesting to learn the context and sequence of events which led to an F-15 being shot down by enemy fire.
(In 1991, the United States relied on the F-117 Nighthawk to penetrate Baghdad and launch salvos against radar and SAM sites. Simultaneously, Tomahawk cruise missiles were fired against similar communication and defense sites. In this war with Iran, the F-35 and B-2 have been used for stealth missions).
Recall that the Serbs shot down a Nighthawk when they were in a similar situation to Iran. They kept some good AA missiles in reserve and used a system of spotters and just waited for an opportunity. Its likely that similar tactics were used by Iran.
Also recall that the Houthis, armed and trained by Iran, gave F35s some close calls over Yemen.
The story is actually quite interesting. The Serbs observed that a nighthawk would routinely fly the same route but their radar couldn’t lock on it unless the missile hatch were open, which they managed to elicit.
In short, it took 2 rare events to occur for it to happen.
This isn’t unexpected for anyone in the actual military: they’ve planned for this for decades. A couple of friends served in the previous war and they mentioned that this is what their training exercises were like: same enemy, same difficulty.
(In 1991, the United States relied on the F-117 Nighthawk to penetrate Baghdad and launch salvos against radar and SAM sites. Simultaneously, Tomahawk cruise missiles were fired against similar communication and defense sites. In this war with Iran, the F-35 and B-2 have been used for stealth missions).