Well, people having done both claim the conditioning in wrestling is more demanding than in boxing.
(IN GENERAL) The cardiovascular system of a boxer is tenfold better than that of a wrestler. The wrestlers explosiveness, strength and muscle endurance however, are all extremely better than the wrestlers. This is simply because boxers run and train to fight long winded rounds, with small bursts and flurries of power, whereas a wrestler/grappler will train for strength and muscle endurance in a HIIT style formula, because they use explosive movements and they might have 5 matches throughout 5 hours, but they have 50 minutes break between matches. A boxer can probably outrun a wrestler, but a wrestler will outlift a boxer (out lift in terms of weight and of endurance) every single time.
The reason MMA fighters gas when you rarely see high level kickboxers/Nak Muays/grapplers gas, is because you are only using one form of fitness in these other styles of fighting. MMA isn't more DEMANDING by any means, it's just working so many muscles that it almost shocks your system by how often you'll switch from explosiveness, to straight out lifting strength and so on.
Y'all should check out the F13 forum, some great knowledgeable guys who talk about alactic, anaerobic and all that jazz that I haven't bothered delving into yet.
My personal observation and opinions based on little citations but rather from acquired knowledge:
- BJJ is a lazy sport. Until the high levels, people train as little as they can, and have an excuse to eat as poorly as they can even if they don't realise they aren't really burning that many calories.
- Wrestling is a strict sport. But it's so strict that only a miniscule amount of people will ever reach the high level of sport where intense training is involved.
- Boxing/Kickboxing/Muay Thai can be either lazy or strict. The person training can push themselves, or limit themselves.
- A general observation I've made is that strikers are generally very good at strict dieting, whereas a BJJ guys are lazy, eat whatever they want and follow the whole "any weight, all skill" ethos.
- BJJ guys smoke cigarettes. I think it's because BJJ is attractive to the average Joe, whereas Wrestling is elitist and most guys dont like getting punched in the face for 12 rounds.
TLDR; To sum this all up, you contradicted yourself when you said, "claim the conditioning in wrestling is more demanding than in boxing", you said it yourself. CONDITIONING. It's simply whatever you are CONDITIONED to.