I have the 600 tc, the 400 4.5, the 70-200 and the 24-70. I use to take them all with for any shoot even for a weekend because I wanted to be able to cover most of the focal range. Even with two body camera, I found that it was difficult to be ready for some situations when something interesting showed up too close and did not have time to have the correct focal lens on the camera body. Last Summer, I was in Newfounland and I missed a lot of shots because of not having a big zoom. when it was announced, I ordered it even I was sceptical about the quality of the lens. I have being using it a lot. I go every weekend to shoot birds and I always carry with me the 600 tc attached to my Z9 and the 180-600 attached to my Z8. With this combo, I have not felt the need to reach to my bag for another lens and dont feel the need to change lens. Now I don’t regret buying it.
I am going back to Newfounland this Summer, leaving in a week. I am organizing my photo bags. Definitely, the 600 tc and the 180-600 are going with me. Since I am going by car I will take the 24-70 and the 70-200, for the low light situation, landscape and environnemental photos. I am still not sure about the 400 4.5 that I like a lot.
That is me, the way I feel about this lens which I am going to keep until Nikon comes with a better quality zoom, or a 300 2.8 tc (hopefully) and then maybe I will keep it. I take it with me on hike and I found it very useful when I get rewarded in the wild with an interesting subject.
But, for me weight is not a problem, I always shoot handheld with all my lenses except when I want to take a video, or doing long exposition. We are all different and this lens suit my need.
I can give you a small advice, if you feel your subjects are always at some distance and you don’t need at all less than 600 mm, in this case there is no need for you to keep this lens. But if you shoot videos ( in your case on tripod) and you do some landscape which I found this lens so good in some landscape composition, then maybe it is worth keeping it, specially this lens is quite a good deal in price for what it offers.
Lina