Waiting 1-2 sec before you start your rotation is less of a loss than waiting during it for your tank to get aggro back.

Tbh it's probably your tank..even on t9 golems I hit the green one straight away with HT to get it in and my tank has no problems with aggro.

I don't understand why you want to be at the boss before your tank lol..just run in slightly behind them..then you can save gap closers for more important things