Your home loan offset account is saving you 2-3% depending on your mortgage rate. Money in an etf might earn you 7-10% per annum based historical figures. Nobody can predict the market so if you were to invest right now it might loose 10-30%… or could go up.
It all comes down to personal risk tolerance. A guaranteed 2-3% return on money in your offset may seem pretty good right now. Especially if you think you may need the money in the short term.