Kodi (formerly XBMC) has a working YouTube plugin now (it was broken for a long time), it indeed works very well from a media-centric interface on the Raspberry Pi 2, including with full HD 1080p video streaming flawlessly over Wi-Fi with a USB adapter. There are plugins for other video sites too. You can run Kodi either from Raspbian or via a standalone distro such as OpenELEC.
YouTube from a web browser such as GNOME Web (formerly Epiphany) on Raspbian is less impressive, don't expect high-definition video from that.
I suppose it depends what you mean by "flawless YouTube". If you must do it from a web browser like a PC then it's not really up to scratch for HD video. However, if you are happy with using YouTube from a media centre interface, then the Raspberry Pi 2 is a good platform for it.