I feel that both warpriest and swashbuckler should not be given blanket access to fighter only feats because it gives away one of the fighter's few things that only it got.
This is similar to the thinking that all rogue talents should not be given away to slayer or investigator.
In general, giving away those special features and giving access to all of the features the parent class has leads to situations that weaken the viability and uniqueness of the parent class.
Also, while obviously the goal is for all classes to be well balanced, it also makes it difficult to re tune or give goodies to one class without the other. For example, because the ninja gets all rogue talents, there is no way to help better carve the rogue's niche in relation to the ninja by giving special rogue talents because the ninja can take those anyway.
It also means from now on any cool interesting abilities that would be good for a rogue must be balanced for both it and ninja.
An example from this playtest would be creating new powerful fighter only feats for high levels should not be impeded because a medium casting class is already pretty strong at that level and they can take it too (warpriest).