But in seriousness i think why they added shin/metsu shoryuken.
Metsu hadouken wouldn't be really a cool final smash.
It's just a big fireball and it's meh. Even if ryu may use the beam one in MvC, it's kind of rip off of samus one.
Ryu use also hadouken in ground often. And it may be dodge easily.
Shoryuken fits well imo for it can hit high and such.
And if you are near of ryu using final smash, you can't counter or block it. It's fit for me.