Its not about the quantity of fuel you can produce. Its about how much “net” energy you can achieve from the processed wood. Now it gets a bit complicated.
How much you get from chipping, depends on your equipment. How much will be able to process and keep verses how much that will be not usable. How much energy does it take to run the chipper. If you are going to fuel it with a gasifier might as well just charcoal the fuel in the first place. With the chipper you are limited to what you can put into the chipper. Charcoal it really dont mater as long as you can cut it up to fit your retort / kiln.
Drying the fuel from green wood that can be chipped. You may need to create a drying kiln to keep up, if you plan to run this around the clock for 3000 hours. Charcoal you dont need to do this.
Then you have build complexity. A direct wood gasifier will be 4 times more complex than a simple charcoal gasifier and that’s not considering automation. For hands free operation there is no way around automating the unit. Charcoal does not need automation as they run much more stable.
Charcoal will consume more energy to produce the charcoal then raw wood feed stock. However, you can get that back by adding water drip. You can also add in raw fuel feed stock with the charcoal as well if your build is capable. Even so this will still be far less work to build than a full blown engine grade gasifier.
My experience with producing charcoal over chipping wood is I can produce much more charcoal than I can chipping wood. Charcoal I don’t have to run a chipper. I just chop up the fuel to fit the retort. I have no limits of what I can use as I can make just about anything fit that retort / kiln. I dont have to run the retort either. Once the fuel is processed to fit the work is done. Screening the dust out is easy and can be done quick if you had a simple screening system.
Chipping is not just chipping, drying and chucking fuel in the gasifier. You must sort that fuel and get all the small fines out, it must be uniform and you are going to throw a lot of it away.