There is a world somewhere between reality and fiction. Although ignored by many, it is very real and so are those living in it. This forum is about the natural world. Here, wild animals will be heard and respected. The forum offers a glimpse into an unknown world as well as a room with a view on the present and the future. Anyone able to speak on behalf of those living in the emerald forest and the deep blue sea is invited to join.
one more thing, you wrote "When you see Amur tigers of that size all the time, it no doubt will have an effect. For you, it's clear that captive Amur tigers are the largest big cats by a margin"
Its not like that, as I wrote, white begal tigers are of similar size. Well, I have seen just 2 white bengals...one was 220 kg weighteed (pure muscle!), the other one was over 250 kg (250 kg weighted at the age of 3), I think that his prime weight is going to touch 300 kg mark.
Difference: amur tigers are definitely longer and with more slim bodies. On the other hand, there are amur tigers who are bear like creatures - overall very robust animals.
When it comes to comparison between amur tigers and lions, Id say, that amurs are obviously bigger, but huge lions are comparable to average amurs. Another difference is that amurs are longer, but lions have more robust bodies. On the other hand amurs have obviously stronger legs.
It seems we roughly agree on the essentials of captive big cats. Amur tigers are the largest captive big cats. Although some are very robust, most males in European zoos range between 200-240 kg. Based on what I have, I'd say that the historic average of wild male Amur tigers (215-220 kg. or 474-485 pounds) could be about right for an average captive male Amur tiger. If Miquelle is right about wild males (about 430 pounds), the difference between captive and wild males is about 50 pounds.
Captive male lions could be 380-420 pounds if from Africa. The Indians seldom exceed 380 in captivity. For their length, lions are quite robust, especially in the chest and neck. If we add the relatively large skull, an average male roughly compares to an average captive Indian male (referring to weights from Indian zoos). Most captive tigers, as you said, are more muscular in the limbs. The front limbs in particular often seem a bit oversized. Tigers also have more flexible spines.
White lions and tigers usually are larger and heavier. I saw a male white lion in a Dutch zoo some years ago. Cost them a small fortune, but he always drew a crowd and was as large as they come (about 600 pounds). The other male, born and bred in the same facility in South Africa, almost compared. The male white tiger in the same zoo lacked about 50 pounds, but he was very robust as well.
In captivity, very large male lions can get to 600-620 pounds. At that weight, they are not obese. Very large male tigers are a bit heavier (up to 700 pounds), but they have different proportions. The difference between both cats is that tigers, in spite of lower numbers, do it more often.
Talking about proportions, The best in this department are Sumatran and Indochinese tigers. In my eyes, they are the largest true cats. Tigers and lions of large subspecies seem different animals. Although cats as well, they're not quite as able as their smaller relatives. Most of the trainers I interviewed considered leopards the most 'catlike' big cats. The things I saw during training were remarkable.