I think that there are a lot of different points here which deserve different answers.

1) First does F need a top tier a la BA Gold? I don't really agree. That is, in principle, what Platinum is here for. Now, you may well say that Platinum is not sufficiently differentiated from Gold on FB (or just that platinum is not good enough), or that platinum is not selective enough (see below) but all those arguments would not necessarily lead to a need to add an additional level, more to a need to repackage them. If saying that a top tier is missing, ten the argument should be that gold and platinum are distinct enough and cater to important separate groups of frequent flyer but I don't get that vibe on this forum (more that people feel gold and platinum aren't sufficiently differentiated or only by withdrawing things from gold).

Incidentally and interestingly, I get the exact same message on the BA forum: that silver and gold are not hugely different and it might not be worth getting out of one's way for gold. In fact, at least platinum is necessary to give you a shot at lifetime status, on BA, you don't even have that distinction.

2) you seem to introduce a distinction between money spent on AF (I imagine you mean AF-KL) vs skyteam and also on flying in worthwhile buckets vs a sgment is a segment. I have some sympathy for both points. I actually think that it never made sense for FB to allow sgment qualification to platinum (most programmes do not have pure segment qualification for their top tier although some do). I also have sympathy with the idea of a minimum share of travel on AF-KL. Note that on the second point, however, while it is more closely usd as a criterion for HON, it is not so for any BA tier, not even GGL/CCR beyond the rather paltry threshold of 4 segments a year. Indeed, it is frequent to have threads by people who 'need 4 cheap BA segments to validate their SCH/GCH/GGL as they really fly with AA or whoever.

3) You mention F lounge access as a perk for this top tier, but here, we might run into some problems. BA does it in broad terms for GCH but have effectively had to create some 'fake' F lounges by name to keep all those emeralds out of the 'real' F lounges at LHR and JFK. They do it more literally at CCR level but despite a much higher threshold than AF-KL could ever consider, this still makes the CCR crowded and participate in an F experience that is much less exclusive (or good) than AF's. So this possible perk raises very serious question, because my guess is that if it is indeed awarded, then the quality of the P lounge will almost mechanically reduce as AF won't be able to sustain the costs of extending the offerings to even, say, 20 additional daily users who are not flying F or paying for the lounge access (that would be a fraction of BA or L numbers).

So to me, the points you make are quite separate and not necessarily tied together. Indeed, they may even call for different answers.