Does anyone know at what point Sephardim became concerned with the concept of Hefsek? This week S&P communities would have read מי כמוך within נשמת. H’ Gaguine mentions the opinions of those that find the addition of piyutim into Tefilah to be wrong. Except that in the case of מי כמוך one cannot argue that נשמת is Tefillah. Even if one objected to the practise of adding Piyutim to Tefilah such as the S&P custom on Tikkun HaTal one would have to highlight that most non S&P kehilot add the extending reshut on Kippur during the repetition of the Amidah.