Not selling the books short at all. Just being realistic about how much of it translates to the sceen. Books 4 and 5 are ripe with slow-burn character development, but lighter than the previous volumes in terms of iconic scenes. Your breakdown is legitimate, and again, I don't see any conceivable way to milk three seasons from that, and next to none of the character's arcs are sufficiently long to fit, even if we get book 6 material in the mix.
Saying that there's lot of plot development in books 4 and 5 is very charitable on your part. Maybe if you're talking about lateral movement, rather than forward progress.
-Tyrion's book 5 travelogue is brutal, and I hope they make some serious cuts/changes to that part of the story. They'll have to, if they want audiences to still like him. Not a 3-season arc by any means. At most, they can have him negotiate his way into an army by the end of season 5, and deal with Dany in season 6.
-Dany playing ruler is a one- or two-season storyline at most. What's the arc? Things are going poorly in the city, Dany ovulates whenever Daario's around, the dragons are let loose and Dany goes off on one of them.
-Jon's story at the Wall isn't particularly elaborate, and could easily fit into one season, but they might stretch it to two, depending on how quickly the other stories are coming along.
-Yes, I'm sure they'll build Ramsay up as one of the major villains to fill the void left by Tywin and Joffrey.
-Cersei has plenty of material, given that we see her in both AFFC and ADWD, and she's strong enough as a character to carry on a 3-season arc, but two seasons is more likely. Probably her bungling things at King's Landing and ending up arrested in season 5, then her maneuvering to get out and likely trial by combat in season 6.
-I imagine that we'll see the Ironborn's power struggle in season 5 and Victarion's trip in season 6, though I expect him to actually reach his destination by then.
-I actually enjoy Bran's story, but it's probably the shortest of them all.
-Connington/Aegon is interesting, but there's not much to the story so far.
-I love Arya and her development as an assassin, but where's the payoff? Three full seasons of training?
-Sansa's growth makes for interesting reading, but isn't very dynamic at all. Arya/Tywin was fun, but lasted only one season, and had the benefit of being paired with Jaqen's killings and Arya's escape.
-Martells: We'll probably find out about Doran's plan for vengeance in the end of season 5, and follow Quentyn's herp-derp in season 6, but truth be told, a lot of it is pretty boring. Honestly, who really cares about Areo Hotah's love affair with his axe, or Arys Oakheart?

I don't need to see every inane detail of Martin's world-building, and character development can be easily synthesized in short scenes on the screen. As far as actual events, fitting books 4 and 5 in two seasons is more than enough time.