I agree with this completely. I can't imagine any person who is a Trek fan to forget something as basic as the Starfleet pennant some where. Has there ever been a Federation starship in any show or movie of any series that did not have the Starfleet logo somewhere on the ship? Also, you can't put your fleet logo on the ship.
Unfortunately it is an oft overlooked decal. I can imagine it presents issues lining up correctly with ships that have interchangeable parts, but, considering the Chimera has none - it would be very welcome if it was added.
The original design has far more details, specially the bussard collectors and the connection between the upper and lower nacelles are looking dull on the ingame model. But thats the price you pay to make STO running on low end computers i guess?