My take on it:
Yes, it should have a built in charger, USB micro or C input, preferably with MPPT type conditioning so that it can be connected to anything from a small solar panel to a high power 2 or 3A connection.
After that, I see it as optional. Those who want to then use it as a power bank could take out some or all cells and put them into a lightweight inexpensive powerbank housing to charge up their mobile or tablet etc, or put into a more suitable lightweight torch for backpacking.
Whilst charging up another set of cells at the same time. I.e. four cells total could keep this setup working fully, 2 charging in the lantern, 2 in use elsewhere. Or all 4 to keep the lantern going for a week or so. Or two sets of four, and a big solar panel.
More flexible than having the powerbank circuit built into this heavy lantern.
But if the powerbank output can be done at minimal cost, complexity and development risk, by all means go for it.
To me, the powerbank output only makes sense in combination with solar input, for those who want to run totally “off grid” or survivalist, but a decent portable panel will cost as much as this torch. I don’t see too many making much use of this. Just plug it into the car, or the mains, or take a spare set of cells.
If the cells are not going to be charged by solar in a minimalist arrangement (lantern + solar panel) then what’s the point ? If vehicle or mains power, or solar (not directly connected, my campervan has 200 W of solar) is to be the source then easier to use a separate charger.
TBH, a straightforward lantern with no charging or powerbank circuits would suit me better, at the right price. If it could also accept primary cells (e.g. alkaline AA etc. in a carrier, 3S or 4S), even better.
Much as I like the idea of spending weeks or months in the wilderness, off grid, not even a motor vehicle to charge from, it’s never going to happen for me, and when I do wander off for a week or two, I don’t take a heavy lantern. Or anything powered only by Liion.