Gentlemen,
Just tested this with the help of Tacview (recordings available on request), running the latest DCS Beta branch as of this posting.
Loadout: 2x ET's. Full internal fuel. No external stores. No pylons.
Configuration: Flaps DOWN, Gear DOWN, DLC DEPLOYED, Hook DOWN.
Then I pitch/power for level flight and ON SPEED in the E-bracket, or 15 units AoA. This corresponds in Tacview to 10 degrees AoA.
With an aircraft I've spawned in the air, it stabilizes around 140 KIAS. In Tacview, the Kinetic Energy readout shows ~260. Fuel flow is ~5000pph/engine.
With an aircraft I've spawned on the catapult, it stabilizes around 160 KIAS. KE readout in Tacview is ~360. Fuel flow ~7000pph/engine.
This discrepancy, subjectively, feels even worse when trying a Case 1-esque approach. Maintaining desired descent rate feels like it takes a lot of extra power when in the groove, and due to the extra speed I'm having to bank excessively which results in substantial sink and destabilization when rolling out on final. I've seen speeds in excess of 170kts in the turn and, again, around 160kts to stay on-speed during final approach.
Unraveling this mystery should be a top priority. If carrier launch is affecting the fundamental lift, drag, and/or weight of the aircraft, then this bug might manifest itself all over the flight envelope for any aircraft launched from the deck. Further tweaks to the flight model might be in error if they're predicated on an underlying glitch such as this.
Update
---------------
Upon further experimentation, it seems this phantom drag or weight compounds with any existing stores. I tried a heavier loadout of full fuel, 2x ET, 6x AIM-54C, 2x AIM-9M (about 96% of MTOW). Level flight in the configuration specified above requires ~155kts for an aircraft spawned in the air, and ~170kts for one spawned from the carrier catapult. So, in essence, it may be a decent approximation to say any aircraft starting its mission from the carrier may be potentially performing the majority of its mission as if it were heavier than MTOW...