The reason we're having this debate is the dichotomy between the wars we plan to fight and the wars we have actually fought over the past 2 decades. The military, by nature, assume 'worst possible' as the target scenario - therefore, in FJ terms, we press for the best we can get to give us some semblance of capability in the 'near peer' arena. This is eye wateringly expensive, and means you cannot afford to replace your legacy platforms on a one-for-one basis. However, just because you can do high end doesn't mean these expensive, and increasingly rare, Gen 4.5+ platforms are best suited for the low end - either in capability terms or cost-effectiveness. Curtis LeMay once opined, about Vietnam, that 'if you have the power to stop a big war, certainly the same power ought to be capable of stopping a small war'. This sentiment stifled the development of tactical aircraft for a generation and led to a high loss rate over Vietnam as the 'high end' F105, F4 and B52 proved somewhat ineffective and vulnerable. The West attempted to fight recent wars using the same maxim (perhaps with the notable exception of multiple reprieves for the A10...until recently..) but we still have had usable reserves of legacy platforms. This (for the RAF at least) will not be the case in the future.
Therefore we are at something of a crossroads. Do we go all-out 'high end' and risk burning them out in a high-rate low-intensity conflict (eg AH64 / C130J over the past decade) or introduce a "Day 2+" fleet of combat air equipped to survive in more benign environments yet still capable of delivering weapons (and surviving the SA threat) when supporting TICs?