I'm extremely aggressive with all games I play, but I've only broken one controller; a Wiimote. And that was through old age -- there's a little plastic thing stuck at the top between the batteries came off. I've had my GCN controller for literal decades, and besides chewing the plastic off the control sticks due to being young, they work perfectly. I got a pro-controller in 2005 too, which fit my Dad well because of his bigger hands and is now my controller of choice because of my bigger hands, and that has survived perfectly.
3DS' are bloody sturdy things, though. I can't EVER see one breaking, and the only way a DS has every broken (not even mine did, but from asking other people how their systems broke and from searching it up on the internet), they always break by someone grabbing the top of it and having a pulling fight over the system. As long as that doesn't happen, your 3DS will be safe.
I even did the thing where you put a little coin under the circle pad for breeding purposes in X&Y; I was worried beforehand, but literally nothing has become lackluster about the system's response or anything. I play a lot of games quite aggressively, as I get REALLY into it, and the system is holding up fantastically. I don't think a regular game of smash could do any damage to it at all.
If you decide to play smash irl, however, you may run into some issues...