1)Bheeshma was wrecking havoc on pandav army even on day 10.Then arjuna placing shikhandi before him attacks bhishma(in the citation it was already mentioned that bhishma was not shooting arrows towards shikhandi).Then all pandavs do the same as well.Then srinjayas also start attacking him and bheeshma attacks them back
2)After this arjuna again keeping shikhandi in front of him cut's off beeshma's bow please note there is no mention of bheeshma attacking arjuna back here
3)seeing this act of arjuna kaurava warriors proceed towards him and panadavs warrior's proceed to protect arjuna and battle take place between the two sets
4)then shikhandi attacks bheeshma and his charioteer again no mention of bheeshma attacking him back
5)Then again bheeshma tries to pick up a new bow and again and agian arjuna's cuts them off .This is the only time when its not mentioned that shikhandi is ahead of him the only time where arjuna manages to cut of bheeshma's bow based on his skills alone and without using shikhandi.
6)Then seeing his bow getting cut again and again bheeshma hurls a dart at arjuna which arjuna again cuts off completly based on his skill
7)After that bheeshma wishes his own death and arjuan starts attacking again without shikahndi this time and bhishma attacks arjuna back both are equal in this duel
8)after this arjuan places shikhandi again in front of him and starts cutting of bheeshma's bow and attacks him more again at this point there is no mentioen of bheeshma attacking arjuna back like there have been in previous cases.It is at this time that bheeshma appreciates the fierceness with which arjuna shoots his arrows
9) after this bheeshma again does attack arjuna probably at this time shikhandi is not ahead of this and arjuna cuts of bheeshma darts,swords and shield's
10)then yudhishtir encourages his army to attack bheeshma and they do
so yes definitely shikhandi was not ahead of arjuna all the times there were some times when arjuna did manage to injure bheeshma without shikahndi but majority of the times arjuna did use him as a shield