The words "perfect" and "thin" present are not very precise. I can cut 1mm bass wood with a 1.6W with 2 passes. Thicker takes more and the char can effect the kerf width. Having an air blower helps.
You must understand that focus and beam shape are major factors. The 5.5W have traditionally been worse than 1.6W. 2.5W is in between. I am unfamiliar with the greater than 5W but the published specs hint that they might not work at full power.
I do not trust the specifications published by any of the Chinese vendors found on EBAY, Banggood etc. You can get better quality at a higher price. Look at Endurance for example.
Typical hobby grade plywood has glues that are difficult to burn. Look for plywood that is made specifically for laser cutting.
CO2 lasers are significantly better at cutting whereas diode lasers are better at etching.
