My point is that you can't reliably know how much charge you have left as battery deteriorates over time. Having a replaceable battery is a benefit no matter how you look at it. Lithium Ion batteries like sitting in the middle of charge for storage purposes, anything else degrades their life and performance. Once battery fails, and it's a question of when not if, you have to throw away high quality bike light for no other reason than them building planned obsolescence in the product. And I am not going to go deeper into just how much better 18650 is than cells used in this light are. From thermal dissipation, performance, over and under-voltage protections, etc.
Two hours might be enough for you and your location, but for mine it's not, especially in the winter when it gets dark before 5pm. People living further away from equator have even less daylight, so longer battery life is always more convenient if for no other reason then to charge it fewer times.
Oh, and dynamo adds far more weight and price than just picking up the right bike light and one extra battery.