AKJ, you're using some incorrect ship launch dates. The TNG:TM does indicate that the Galaxy's design phase was decades, but this does not mesh with the on-screen canon, which is superior and overrides the TMs in any conflict, and has the Galaxy class launching in 2363. Furthermore, the Intrepid launched BEFORE 2370. We know that the pathfinder USS Intrepid was in service in 2370, and that her CEO engaged in regular competition with Geordi over reactor efficiency. But the registry number of the Intrepid is NCC-74600, just under 400 numbers higher than the registry of the NX-74205 Defiant, which was designed in 2366. The USS Intrepid likely launched within a year or two of the Defiant, though it may have had a longer development time between the entry of the prototype into the registry and the actual launching of the pathfinder, putting it's launch date somewhere around 2368, not 2370. The Intrepid is really only about 5 years newer than the Galaxy class. To say that the Intrepid outperforms the Galaxy is comparable to saying that a 2010 Ford Focus will outrun a 2005 Ford Mustang. Or better yet, it's like saying that the
Worcester class Light Cruiser is comparable to or superior to the
Iowa class Battleship because it is five years newer.
The Intrepid is faster than the Galaxy class, and she performs the role of a short- to mid-range Light Cruiser better than the Galaxy class, but one-on-one, an Intrepid is not a match for a Galaxy class in anything but a race.
As for the Sovereign being the successor to the Galaxy... Rick Sternbach himself, one of the ship's designers, has stated that the Sovereign was designed to replace the
Excelsior as Starfleet's premier, workhorse Heavy Cruiser, and NOT to replace the Galaxy class as her premier Capital Ship.
Typically, Starfleet ships tend to have a 'primary' lifespan, in which they fill the role they were designed to fill, of about 20-30 years, give or take, and that's about how frequently we see Starfleet produce new ships to replace its premier capital ships.
Oh, and on the advancement of Trek tech, the rapid advancement of computer technology today is a poor judge, because computer tech is not a mature technology. Moore's Law of increasing computer power is not an eternal 'law', it's just a description of the rate of advancement we've been running at, and a rate that we cannot sustain. We have already been running into major walls in the last several years because we're smacking into the limits of what we can do within the laws of physics. The rate of acceleration we're at in computer power is only being sustained today because of gimmicks and tricks that we're rapidly exhausting, and in the next ten to twenty years (at best), barring a major revolution in the very nature of computer technology and how computers work on the fundamental level (i.e. the introduction of quantum computers as a viable system), computer advancement is going to drop from exponential growth to marginal improvements very quickly.
A better tech to compare to is gasoline engines. The performance capabilities of gasoline engines has not really increased drastically in several decades. By WWII, we were already hitting peak horsepower outputs. Later advancements allows a few leaps forward here and there, particularly with the advent of computer tech and increasing electronic controls, but aside from the introduction of fuel injectors, there hasn't been a truly significant advancement in gasoline engine tech in 60 years or more. The rest of it has been marginal increases in performance and a bare handful of special-case advances. That's what you get with mature technologies. And the technologies in Trek are VERY mature. Most of them have been in use for several decades, if not centuries by the TNG era, so rapid leaps forward are going to be very rare.
