K11, is just your dislike of Speedtree or the planting itself the bothers you?. It bothers me as well but don't know how to make it better, never really enjoys the vegetation part of course making.
To be frank, both - though my bother should in no way be a concern of yours. I would have identified the foe as "Speedtrees" if it were just a Speedtree issue in this case. In your 3rd image they immediately attracted my attention - and a bit of immersion difficulties. Aside the Speedtree issue (don't get me started on that, clumpy tree blobs etc) they looked a bit out of place, not to say unnessary for this particular course with its many, lovely undulations.
I do not know the original Links Nautilus. I suppose that if you port it into CF you would also feel obligated to replicate its vegetation as closely as possible. I don't know if you think you've succeeded or if you had to make compromises - but we do have a very limited choice of tree model in CF-Land at the moment and no real prospect of this situation getting any better soon. The Devs will probably ship CF with a bare minimum of trees at the start (possible treepacks to be added at a later date) and whoever needs something extra is on his own.
Could well be then, highfade, that these trees, right now, really are the best you could do, given the lack of choice.
It still could be just me, though, and perhaps I simply missed an opportunity to STFU. Wouldn't be the first time and I'm sorry if this somehow rubbed you the wrong way. But you confessed to being a bit bothered yourself and all I can say to that is: "Good, I'm glad you are!" Everybody should be bothered by these trees, imo - though I would not know how to solve the issue. Of course I could try to interest you in Blammocorps! latest crop of links plants, but these, too, are quite ridiculous in their own right, albeit in a different way.
With regards to Speedtrees (and the Unity 5 trees K11 built?), the biggest issue from my untrained eyes point of view is how the shadows work (or don't work) between the leaves. This makes the trees very dark on one side which just looks unnatural. In the next Unity patch, 5.3 set for a December 8 release Speedtrees get improved:
Trath, you just pointed at something that both Unity Trees and Speedtrees refer to as AO. Ambient Occlusion. More AO means darker shadows and translucent, brightly backlit leaves when the tree is standing between you and the sun. AO adds realism, they say. But unless there isn't the brightest of sunshine, in my old eyes at least, trees are rarely that extreme in contrast IRL. They have darker and brighter areas, in a more gently and diffuse kind of way, due to the natural irradiance of light and their partially transparent leaves inundating each other with a minimum of light. So toning the AO down might be in order, but only at the expense of the trees easily looking a bit washed-out. I do not know nearly enough about this to propose a productive answer. All that I can say is that I am very aware of AO and of the self-shadows sliders of trees when fabricating one of my crippled little Unity tree editor bastards.
I do know, however, that computer golf games through the ages have suffered from varied tree issues, each in their own way Let's face it, trees are heavy on the performance budget and will always look a bit weird no matter what. So it's official, I'm afraid: We are having a tree problem, here. PG is as much a helpless victim of this perennial scourge indigenous to computer golf as we all are, and there is not really much we can do about it, - except design a lot of treeless links courses, where they won't be missed. On the design end, it's a constant struggle - a bit of the elephant in the room. But it is what it is and there you have it...