According to List of battery sizes @ Wikipedia, maximum dimensions for the 26650 format are 26.5 × 65.4mm, whereas for 18650 it's 18.6 × 65.2mm (!).

To me it is clear that 26.8mm cell diameter is a little bit out of spec, but not too much. If I were the chief manager in charge behind battery tube design and specifications I'd probably add an healthy extra 5% cross section to that figure just to be safe. This means I'd bore the tubes to a diameter of 26.5 × √(105/100) = ≈27.15mm. Even if I were to only add a 3%, my bore diameter would still be 26.9mm.

Just measured a spare unused dirty pair of LiitoKala INR26650-50A cells I have inside a drawer, ∅26.8mm.

Forcing? Struggle? You speak like if it takes a lot of effort to make the cells go inside. Aided with some sort of stick, fork or spoon you can easily slide a single cell along the entire tube to test how tight the fit is and check the wrap integrity. If fit is too tight and/or the wrap gets damaged, I'd rewrap the cell(s) and fix the tube or use other cells in that tube. Finding solutions it's all about.

Next time ask your flashlight maker to leave tight-fittings for you know what.

Cheers