It is very important to select the right song for stage shows.
I think Hema's selection of song ( Bachna e hasino) was incorrect choice. Kishore da has sung this song and his voice was very thick with very superior tonal quality.
Unless someone has this voice quality he shouldn't attempt such songs.
For that matter we can see that whoever tried to sing Kishore da's song ended in disaster, examples:
1.Saptak :'ye jawani': got eliminated
2.Debo : Rimjhin gire sawan: saw Rajiv getting selected over him: AS commented, it sounded as if mukhda was sung by Kishore alike & antara by Debo
3.Hema: Bachna E hasino... we all know.
4. Rajiv: Roop tera mastana( I've not seen in UK) but people present on show told he was unimpressive.......
I think AS's guidance is vital at this point, he is very experienced and seasoned.