Except for FBW Airbus, planes are trimmed for a speed, not an altitude. Flying along straight and level at 250 KIAS, ADD power to increase speed--what happens? The plane, whether a C150 or a B747, begins to climb in an attempt to maintain its trimmed speed. Pull back the throttles and it will descend.
Power + Attitude = Performance
Trent OK, trimmed for take-off, pour on the coals, what will happen at about V2? It should, discounting any negative angle of incidence, lift-off and try to maintain V2. Why didn't it lift off right away, you say. Because it hadn't reached its trimmed speed.
Airbus FBW is G-stable, not Speed-stable, so pitch controls speed doesn't apply. Please refer to M. DesCartes for reasons why they did that.