For incandescent replacements, I agree with "dischargecraze", the filaments could not be beaten.
Such flat glass substrate COB may be cheaper, but it will be never optically compatible with the incandescent filament, so in many fixtures the retrofit will be problematic.
Plus it requires vents, so a path for dust to enter impossible to clean spaces (inside the cover).
The filament style design uses the smooth outer surface as the only interface towards ambient air, so naturally good convection around (within the possibilities of the fixture) and no places for the dust to accumulate.
For the dedicated designs, either a plain PCB with a lot of low power SMD's for a low intensity, or an IMS board on a heatsink for higher intensity applications will be way cheaper and more efficient - usually the light is required in one half sphere only anyway, so you design the board according to that, saving the optical losses compare to the incandescent fixtures.
With retrofits you never know, what is the required direction, so you have to shine all around, but when you design a LED panel for a dedicated lantern design, you already know it, so may orient all directional components accordingly.