What are the advantages/disadvantages of a continuously decreasing block reward compared to the current method?
The main advantage of the staircase rewards is simplicity. It's easier to implement; easier to describe; easier to plan with.

The main disadvantage is that it is less mathematically elegant. It will not be very disruptive in practice because it is known in advance and can be planned for.

The early adopter advantage is not a consideration, as it can trivially be controlled with the timescale parameter.