^The Stargazer was never described as being a science vessel, much less underpowered. The Tsiolkovsky or Lantree might have been described that way...
I dont recall if it was worded this way in the final episode, but from the Relics script:
PICARD
The first ship I ever served
aboard as Captain was called the
Stargazer... it was an overworked,
underpowered vessel that was
always on the verge of flying
apart at the seams. In every
measurable way, my Enterprise is
a superior ship.
(beat)
And yet... there are times I miss
that cramped little Bridge very
much.