You do not have to be the fastest, but you do need to be in the general speed range. Unfortunately, newer teams have fewer choices so speed is usually the most viable tactic.

I am gold 4 and my teams consist of 7 different champs that run the range of 142 to 225 speed (the 142 is a Skull Lord I sometimes use loaded with loads of HP and a shield set giving the rest of my team a 35k shield). But generally my speed is 177 to 225 plus speed aura. That does not usually make me first in a fight but it usually keeps me close enough that i am not lapped by a speed focused team (except skull lord he is just there to look menacing provide that shield and reduce their max hp when they hit him).