You tend to find that in most live situations most acts need about 4 songs to hit their groove. That's why all those "live" "credible" "authentic" shows have multiple run-throughs before hand. Later with Jools Holland? Multiple rehearsals and some clever editing to make it look like five acts just played in the same room flawlessly. Album de la semaine (French TV show)? Acts record about 6 or 7 songs then repeat the first three at the end of the set, and again if still ropey. The show picks the best seven takes.
I'd rather have a well filmed, musically edited and mimed performance (with crowd noise and the acoustic reverb from the studio - Pepsi Chart Show was good at this) over a badly mixed, vocals too present, band instruments way down static camera live TV performance with all the energy of my nan slumped in her armchair. It's not like T4 had the budget to pay their studio staff all afternoon, sorry Dannii, you can't do another take, V and The 411 are up next.