I'm afraid there is no way to flood fill the grid for all pupils and all subjects.
There are a couple of options that might save time when entering EYFS data. On the Enter data screen (Enter Data --> School Assessments) you can copy the data from a previous term. That way, you may only need to change a few judgements which differ from a previous set of data.
If you are using the statutory results page (Enter Data --> Statutory Assessments) you can copy data from 'Main Assessment' to save entering results twice. Insight can input 'Emerging', 'Expected' and 'Exceeding', just click the 'Copy Main Assessment into EYFSP' button at the top.
I have passed your idea about making 'Expected' the default for all children onto our developers. Thank you for letting us know what you’re looking for — most of the improvements we make come from ideas and suggestions like yours.