Alright so I've played this game a lot and I've also played smash a lot. Before I finalize this into an article, here's what I've got on Smash verse Royale.
Ring-outs verse Supers:
In smash you can attack a character as much as you want but the only way to score is by knocking them off the map. Similarly in Royale only* super moves can kill. What makes ring-outs great is trying to get back on the platform. After being smashed off screen it is always impressive to come jumping back. The downside of this is you can only come back so many times before you are knocked out. In game this equates to you feeling your death come closer and closer with every hit and you can only prolong the inevitable. This also means you see your death coming, there is no shock value to being killed (unless everyone sucks and is at 300% damage of course lol). Royale is very, very different. Without ring-outs there isn't the joy of jumping back to safety. In its place there is the joy of screwing up a persons super. For level 1 supers this means punching them first or rolling out of the way. For level 2s it's all about using your own super to stop them. Level 3s are all about dodging and can be just as fun as jumping back to a platform depending on which super it is. In Royale another difference is death can happen at any moment. This really speeds up the game and makes it more hectic. I'd defiently say Supers work better than Ring-outs simply because they are crazy and all over the place. In Smash it would be like letting people spawn a hammer whenever they wished; it's awesome.
The metagame:
On paper Royale seems like a bad idea (no damage, wtf?) but during gameplay it is flawless just like Smash's health percents. I'll just consider both a tie on which works better. That is until we factor in the depth of each. In smash you have two options: attack and cause damage or eat food and heal. Royale really shines here because it has its equivelent of attack damage and food but it also has throws. Now you know Smash has them too but in Royale they work differently. A throw knocks out 10% of a persons AP instead of giving you AP like a normal attack. This really spices things up. Also you can't talk metagame's without factoring in that deaths in Royale don't make you lose AP. This both streangthens and weakens Royale's metagame. Regardless I'd have to also give this catagory to Royale since it is as simple on the surface yet it goes deeper.
The characters:
Smash wins, that is all. Sure Sony fans will love the roster but not as much as Nintendo fans love Smash's roster.
The items:
Smash wins again since its items somewhat replicate Royale's supers. Plus Royale's items are all for the metagame, not for just joy.
The stages:
Smash has a lot but Royale has quality. Every stage is flawless and really shows off Sony IPs.
The final boss:
Without any spoilers, this is hard to discuse. What I'll say is Royale easily beats Smash because it brings together the best aspects of the game.
Single player:
Both are fun but Brawl knocks it out of the park.
Btw I stopped putting that much effort into this halfway through lol.