As a semi pro boxer and pro MMA fighter I can tell you that wrestling is twice as 'tough' as boxing.
This article is a great example of why; wrestling is fucking thankless. If you are seriously good you may get to coach a high school, if you are elite you may get to coach at a university and if you're super elite you may win an Olympic or world medal. And what does that get you?
In terms of physical ability wrestlers outshine every other athlete I've competed with. They are almost as explosive as weightlifters, almost as good at middle distance running as runners, almost as fast off the blocks as sprinters, almost as agile and flexible as gymnasts. While none of those are even close to each other.
For example, I coach a soccer team. It's low level but I have been lucky enough to coach a couple of guys onto professional teams (in Europe). These dudes, physically aren't even close to lads who get smashed in wrestling. They are inflexible, they can't squat, they're not particularly explosive and the sport doesn't test their strength, etc.
The only thing that boxing has over wrestling in the toughness department is getting straight fucking punched. Getting beat around and keeping your head together to defend, keeping your heart together to keep going, etc. That's all tough. And I suppose, for the vast majority of athletes totally thankless. They won't even get to coach high school or college (I mean there is no 'career' beyond how far you can take it, which for most, is not very far).
So it's about sacrifice and reward versus competition. For example, Rugby is a fucking tough ass sport. You need a huge range of attributes to excel, but if you play in Ireland or Wales you are probably going to be rewarded all the time. You'll have plenty of matches, you'll get time off school, you'll get amazing facilities and huge support. On the flip side, if you are a wrestler in Ireland you get no rewards, no funding, no support from school, or friends, or employment but you will be expected to train harder, for longer, than the majority of rugby players.
What I'm getting at is simply this ... all sports are easy. Because all sports are enjoyable for the most part. What fucking sucks is walking into dingy little underground gyms, at 6 a.m. in the freezing cold just to get your ass kicked, and every day you do no one is noticing, no one cares and no one supports you. Case in point, the Irish boxer Katie Taylor. She is the most decorated boxer in history (regardless of gender) and is only now getting decent support from her government because she is going to the olympics (the first time women are boxing in the olympics). That's tough.