A huge plus for US platforms is the diverse weapons capability associated with them.
The F-18 will be in service with the USN for some time and is already slated to receive the AIM-260 ahead of the F-35 so Boeing will continue to innovate system upgrades for the next 10 years at least. The fact that they are due to receive the AIM 260 means that the USN carriers will fly the F-18 and F-35 concurrently for some time. For the IAF on the negative side it just does not have the kinetic performance that the IAF wants/expects from an Air Force focused fighter.
The "lowly" F-16 Block 70 offered to the IAF (as the F-21) already has the JASSAM-ER integrated with it. This stealthy cruise missile with a 450 kg warhead has a range of about 1000 km, far outranging the SCALP with it's 560 km range. Poland has just signed a contract to arm it's F-16s with the JASSAM-ER. But in terms of AAMs, it will not receive the AIM 260. So the question is one of priorities. Is the IAF looking for an air to air fighter or is it looking for strike options. A negative with the F-16 is that it is at the end of it's life cycle. And LM is not going to upgrade it further. Given that the IAF is looking for an aircraft to be viable to at least the 2040 timeframe, the F-16 does not fit in. Though it will IMO by far the cheapest to buy and operate.
The F-15 in it's latest offering the F-15EX is a formidable aircraft. 14-15 tons of payload, 11 hardpoints, can be armed with the AIM-120D, AIM-9X, JASSAM-ER and will have the EPAWSS EW system designed by BAE Systems, the same company that has provided the F-35 with it's ASQ-239 EW suite. The USAF plans to buy 144 of them and plan to keep them current upto 2045. Plus they have the kind of kinetic performance the IAF loves, Max speed Mach 2.5, service ceiling 60,000 feet, airframe rated upto Mach 3. And an airframe life of 20,000 hours which is more than 3x the SU-30s. Given the IAF'S above average annual training flight hours per pilot, this long airframe life will be of great value. The F-15EX will also likely in the future get the JASSAM-XR, a development of the JASSAM-ER. The XR will have a range of 1800 km. It will also get the hypersonic boost to glide ARRW weapon to strike targets over 1500 km away at Mach 7-20.
Buying more Rafale will be the easiest but because of lack of economies of scale Rafale upgrades are expensive. However Dassault will keep the Rafale current with upgrades at least until the proposed FCAS is ready for deployment. That will be in the 2035-2040 time frame. Plus in the air to air domain the Meteor is formidable. However the EW suite has not been proven against a networked AD system with long range SAMs like the S-300 or S-400. In Libya the Rafale knocked out a Turkish SAM battery which had a range of 35 km using the HAMMER glide kit with a 60 km range. Replacing SCALP is a work in progress, it's replacement by MBDA will likely be supersonic/hypersonic but deployment time frames are uncertain as of now.