Besides MisterX "HD forests" and simheaven's "Forests", there are other HD trees projects for X-Plane that are currently under development and that I am aware of on good authority. Turbulent Designs is also rumored to be working on a Terraflora version for XP: https://flightdeckx.com/turbulent-designs-terraflora-coming-to-x-plane/
If confirmed, that would be another great addition.
WT3 fully supports Navigraph since version 2, supports SID/STARS and real traffic, offers a great variety of options, can be fully customized (gate assignments, amount of traffic, amount of GA aircraft etc.) and also provides a simple but efficient traffic radar feature, which includes a camera to track each single AI aircraft in the area. If an airport comes with taxi routes already compiled in WED, WT3 auto-generates flights and taxi routes with one single click in no more than 5 minutes for the bigger airport and few seconds for the smaller ones. Otherwise, you can create taxi routes yourself in WED (the logic is no different than AFCAD for the ESP counterpart). For people who are unable to make edits in WED or simply do not want to bother with this, a long list of free customized ground routes is available on the org for most major airports (created by users). Newer scenery releases like KAWO by airfoillabs already offer an install option with static aircraft and another option without static aircraft and pre-compiled ground routes for people who prefer WT3 to automatically populate gates. For the records, most of us keep WT3 traffic to 70% with a negligible impact on frames. Besides WT3, there are several other ground handling products, there is a very nice freeware for pushback, there are at least two airport navigator tools (one payware by Flight Factor for advanced users, one freeware, but extremely efficient). None of them require more time for setting than any other counterpart for ESP, at least based on my personal experience.
Sorry, but I have to disagree again. X-Plane is no longer "the flight sim with freeware addons". I understand there is a kind of consensus within the community about this, I was also misled for long time as an FSX user. There is only one problem: this is simply not true anymore. Things are changing and very rapidly. A great number of 3rd party developers already came or are coming to X-Plane and the quality bar is raising dramatically. The times of Lego blocks and homemade addon aircraft created by passionate simmers "after dinner" are gone forever. Only in the last few months a long list of high quality payware aircraft have been released, from liners to GA aircraft, not to mention updates of aircraft originally developed for XP10 that now fully support XP11 features like PBR, G1000 and much more. On the scenery side the payware offer is even greater. Every day a new scenery is announced for 2018. The same will hopefully apply soon also to HiFi, REX and other developers, if we believe some rumors. There are also rumors about ATC addons under development, although, in all honestly, I am pretty skeptical about this specific kind of products based on my ESP experience. I am afraid that the PilotEdge concept is the way to go in the future for people who require an advanced ATC environment.
FSUIPC is a great tool, but if you want to use it with some 3rd party products, a payware registered version is required. FlyWithLua is a scripting language that allows users and developers to add custom behavior and scripts to the sim. It's completely free. Gizmo is a commercial programming environment/SDK for payware aircraft. It is not needed for the average user, unless you buy certain aircraft, in which case it simply comes built-in.
Honestly, I think there is still a lot of misinformation surrounding X-Plane. On the other side, though, it is true that the sim itself is still unpolished. Despite its great potential (the Vulkan addition sounds very promising), it still has several annoying issues that definitely spoil the user's experience. While night lighting, G1000 and more recently VR support were great additions in XP11, daytime lighting is far from being convincing and is definitely worse than XP10 (especially the backlight effect on trees in really awful). Mesh handling is still very primitive and this is a major limitation for scenery developers. Default clouds and sky textures are poor and only an expensive addon like x-Enviro makes things a little better, at least as long as HiFi will not fill this gap (hopefully). Unquestionably, there is still a lot of work ahead for Laminar and I definitely agree that a "blind eye" is still required in many cases. However, I don't think that lack of 3rd party support is a problem anymore. Quite the contrary, x-planers are now facing the serious problem of the increasing price of newer addons. After all, we can't have the cake and eat it.