That doesn't mean anything though. It still has Toxic Spikes + Spikes, Natural Cure, Leech Seed etc. It is different.
Sure. You shouldn't limit yourself when teambuilding. "I must have these two pokemon on this team, no matter what." is an awful thing to do. Teambuilding should be open and willing to change. Even if I like a certain pokemon a LOT, I won't weaken my teams just to randomly put it on my team. That is stupid. Especially when its not one, but two pokemon.
If Milotic and Starmie work together, then it works. If it doesn't work for you, don't weaken your team by keeping them both on because you "like them."