Bro, Do you really believe that this issue is only about the S-400? The S-400 is just an excuse to put Turkey under pressure and an effort to legitimize the US justifications against Turkey. The real problem is that we resist not accepting the design that is being tried to be established in our south. Which country carried out the lobbying activities of this bill (included the exclusion of Turkey from the JSF), how it justified its request, it is necessary to evaluate such matters also. Lets say Turkey get rid off the S-400... Any guarantee for other concessions demands will not follow tomorrow? For this reason, Turkey has already taken the risk of not acquiring the F-35.
Meanwhile, the strategic value of the S-400 in terms of Turkish air defense system design will start weaken after 2025-26 (SIPER, and the national early warning system). So why are these needs' prioritizing changed? If the air defense system works are more advanced, couldn't Turkey keep its long-term air defense needs on hold?
Turkey need time 5-8 years for long-range air defense capacity(yes, something was not replaced, a nonexistent system was acquired.) and has a gap filler need of approximately 15 years for new generation main combat jets. When viewed from within this risk range; Turkey has a large fighter jet fleet, but more importantly, a rapidly expanding domestic ammunition/missile arsenal.
But the need for the A/D part was more urgent. Why was it urgent? Because this long-range air defense tender, which we call T-LORAMIDS, has a history of almost 20 years. The USA, for some reason, tried to delay Turkey's access to these systems, directly or indirectly. In the end, we started to develop our own system starting from the lowest layer, and during this time, the S-400 system has been an assurance in the hands of the Turkish state in case of any western bloc relationship totally collapse. It is worth remembering that this purchase came after an attempt at an Atlanticist-backed uprising in the south of Turkey, a pro-NATO military coup attempt in Turkey, and an attempt to push TR into a war in Syria.
Another issue regarding F35 combat jet planning is how functional this aircraft will be for the air force of a country whose alliance relations with the United States are at risk of being completely disrupted. In other words, when we look at the developing geopolitical and recent cyclical developments, Turkey's move away from the F-35 supply is also could be Turkey's choice in a way. Or at the very least, it may indicate that the air force will no longer be entirely dependent on (and control) US logistics. Even if Turkey returns to the F-35 program, previous plans such as 100+16 are now completely unrealistic. I do not want to spread the subject too much. Because it is too complex and has many sub-items.
TLDR, the MMU represents a transformation and the goal of full independence for the Turkish air force. We are not far from there. Therefore, we can pass the current risk range without the F-35. It is better in any case than stepping back from our bigger interests and can be ignored.
