1) Tua is from New Zealand aboriginal origins. If you had been there or happened to see them on TV, it's natural (inherited) thing for them to have somewhat more fat than is considered normal for US, Europe, etc. 2) Tua looked completely natural and had a good stamina at 220lb. Reduction of weight would only make it worse for him, reduce his punching power and durability, without giving any advantages (he's not a mover, not a swarmer, that's not his style).
The division was weak. The fact that he was looking bad against an old journeyman (Walcott) and then lost to natural light heavyweight who was also past his prime and old, shows it was no longer the same Louis. Watching Marciano's fight shows he was completely shot by this time, even though he was a top contender. I'm talking about prime Tua, and about a clearly shot Louis. Best weight for Louis was about 200 or a couple of pounds heavier. But clearly not 213 pounds. There can be different periods in fighter's career. Most of Walcott's career he was nothing more than a journeyman (definition of this word was discussed here some time ago). Majority view of whom? Charles' achievements at heavyweight are MEDIOCRE. He was a sure Top 5 light heavyweight (argueably #1), that's where he should be ranked. The approach how many fighters are often ranked is very flawed. Such as ranking Harry Greb at middleweight, despite his main achivements and his common weight being light heavyweight, Mickey Walker's ranking at middleweight, despite him being a welterweight and having a very weak 160lb resume outside of Tiger Flowers' robbery. Sam Langford ranking at heavyweight. Etc, etc. And consensus is a wrong word there, btw. Majority of well-known experts, perhaps, old men who can't stand modern or semi-modern times, it comes as no surprise. You should be aware though of how much critics many placements on their rankings get though. Archie Moore cleaned out the heavyweight division?!? Hold your horses! What weight?
It's not a cultural thing. If you look around yourself, you might notice people, who eat a lot, but don't get fat, while some get fat quick despite all diets and regime. Predisposition on genetic level.
I don't care a little bit about this lineal/linear championship ****. It's a theory that has no practical usage, when evaluating a fighter's level or trying to predict the result of some bout. The guy drew with Dale Hall and Andy Walker a month prior to meeting with Walcott. That's a very clear sign that he was an average fighter. Lost to Dave Whitlock several months prior also. Managed to beat an old shot natural light heavy in Charles (in Layne's home state, wink-wink). But lost to Willie James and Kid Matthews in between. That's because Marciano wasn't proven either. And if I start counting how many times the press (including Ring magazine) was wrong on naming prospects as future champions, I'd get into hundreds of fighters who never managed to achieve what they were predicted. Examples of fighters with proven solid chin by 23, who lose the chin all a sudden after a loss at this age? As good as what? It was completely unproven prior to Marciano fight. You seem to not understand that fighters can change their status several times in their career. Prospect, contender, champion, great, journeyman (as they got older), then tomato can (as they got completely shot). There's no consensus top 20 for Walcott. Walcott had been a journeyman for large part of his career. During the 3 years prior to Layne loss, Walcott lost to both great fighters he met in Louis and Charles, and only managed to beat other journeymen or tomato cans. That's what journeyman is, a good, but not really great craftsman. Walcott was NEVER a big puncher. A tricky puncher, yes, but never a big one. Light heavyweight (pretty much) Satterfield dropped Layne, the test was not passed. Satterfield didn't drop a lot of people prior and after that, but he DID drop Layne. Logic suggests those lot of people might have had better chin than Layne then? Most contenders are journeymen. Good at their profession, but not extraordinary/great. He didn't knock out or even down a lot of people. He had punching power, obviously, but he wasn't a great puncher.
Training for what? For marathon? Stamina is only one small component of being successful at boxing. If you have seen Tua at the Olympic games (where he was stopped by Savon), he looked too thin/small, but at the same time he wasn't ripped either, and it certainly hurt his durability. Again, what would he be training for? Marathon? I can guess Joe Louis could train down to 190, if he really wanted (he did weigh that low early in his career), but he'd have to sacrifice a lot of things. Fat is the source of energy for our body, water is very important also. Sacrifice too much of them, and you will only do yourself harm, not get better.
Because the division was weak, that's why Louis was losing only to great fighters. This subject was discussed, I believe, about a year ago, with photographs, etc. Louis was far from ripped, there was excessive weight clearly visible on his arms and his waist, I pointed it out then, you should remember it. What you mean "worked as"? With Dempsey situation was confusing. He was semi-retired, and thus there was no simple way to evaluate his status as a fighter at the time of the fights with Tunney. There's no point relative to which we could do that. Prior to that fight Johnson wasn't losing to any contenders or tomato cans. By definition he wasn't a journeyman at the time of this loss. If you have ever read Ring magazines with this or that kind of ratings they sometimes compile, even though some things get a top placement, but detailed results of the poll show they didn't get a consensus, they only got a majority. There's a difference. You start it here, and you will have several people (including me) who don't have Walcott or Charles in Top 20, for different reasons. Ratings are subjective thing, and everyone understands the criteria for it differently. Even if just one man out of a million disagrees with something, there is no consensus. It means little. A lot of boxers can win a title for one or two fights, that means little. Obviously we have a different understanding of "clean up" of a division. It will hold less weight than Jermain Taylor's (be it controversial, I had it split, for example) two wins over Hopkins at 160lb. Hopkins never really was a natural middleweight in his pro career. He's more like natural big super middle or natural light heavy, how uses extensive training to get down to middleweight. Same as Jake LaMotta was never a natural middle, for example, but was a 168-175-pounder.