As Co0kieL0rd has pointed out, I am fairly confident, that especially Royal Carriage improves Ranger and Giant a lot. The problem I have with all of these is that by themselves they aren't really worth it. When there are no villages on the board even Ranger might not be worth it at all. I haven't tried Ranger/BM yet, but my guess is that it probably isn't as good as Council Room/BM or Smithy/BM.
Pilgrimage has been more useful if you use Ranger in order to flip the token to prepare yourself to buy it, but in that game where I did that I also hadn't been able to build an engine, so I was stuck waiting for the 3 cards that I wanted to duplicate. I have to admit that I did forget about Pilgrimage eventually since I started to green before I probably did get the cards I wanted to duplicate.
I agree that if there is no way to play two rangers a turn, it's not great. I'm not arguing otherwise.
But I am not convinced at all that Royal Carriage makes Ranger better, at all. If you line up Village and Ranger you're almost forced to call Carriage on Ranger no matter what just to get the token right. If the Ranger was a Smithy, you are a lot more flexible about calling the Carriage while drawing more cards. Of course Ranger is good with Royal Carriage but which drawing card isn't? I don't see the combo. You should really give it a try in an engine, I've grown to love that card after initially not liking it so much.
If there is Pilgrimage and Ranger on the board, I would never use Ranger to set up Pilgrimage if you're playing an engine. Maybe the other way around, one good turn should be much more worth than $4. The way you proposed let's you gain three cards at the cost of a good turn, which doesn't seem right.
I recently played a 3-player game where one of my friends got pretty much knocked out by turn 7 or so when my Giant destroyed his Giant. However, King's Court AND Royal Carriage on the board were what made Giant viable in the first place. I indeed think Giant benefits a lot from those cards. Looking at the average money output of Giant is misleading. What really matters is you get $5 every other play and that extremely helps spiking Provinces and Colonies. Royal Carriage has probably the best interaction because you are pretty much guaranteed to get $5 each time you play Giant and thus to be able to buy a Province. And the attack does matter as well, especially when it trashes other players' cards as this usually means you trash either their Giant or some other key card while spiking a key card for yourself. It's not very likely in the beginning of the game but when it happens they might as well give up.
That aside, I'm not sure I wouldn't have bought Giant had it not been for KC or RC. Whenever I played a game with Giant I usually have been rewarded for gaining it.
Average amout of money is misleading yet you want to play two of them every turn? That's confusing. But still, I don't see why KC makes this great. I can also KC a knight and hit them three times and even mess up an even knight split, still nobody talks about this being a combo since it is usually not more than the sum of its parts. Using it on Giant seems like exactly the sum of its parts, actually.