You would be right, if we are talking about two technologically comparable forces. But the fact is, that rifled breechloaders of 1890th type are virtually impossible for Church to obtain in near future.
Just like it would be impossible for the Church to develop a breechloading rifle in anything less than 2 years? We all saw how well that worked out.
So, against the CHURCH fortification, pneumatic guns wouldn't be "outdated" for decades. And they are REALLY powerfull. One 380 mm shell from the dynamite gun contain more explosive than ten ordinary artillery shells. And the pneumatic gun is much cheaper, easy to produce, and could be placed virtually on anything.
http://www.spanamwar.com/dynamite.htm
However, the disadvantages were greater. Because of the slow muzzle velocity, high gun tube elevation was required unless fired at very short range. The projectile itself had a tendency to be deflected by the wind, limiting the accurate range of the gun. It was not reliable at ranges over 900 yards, which was somewhat limiting. The gun was reported to jam easily, and required several hours work after a few shots before it could be fired again.
The dynamite explosive lacked the shattering power of a standard projectile, and was also sensitive to freezing and bullet impact. The projectiles were fragile and had an usual fuze which frequently would not detonate. The fuze consisted of a steel ball that impacted a series of percussion primers when the projectile hit the target. The projectile was armed in flight when an impeller unscrewed the end of the fuze, freeing the ball. The system, when it operated correctly, created an unnerving six or seven second delay between impact and explosion.
http://www.heliograph.com/trmgs/trmgs1/dynamite.shtml
What finally made the dynamite gun obsolete was the development of new high explosives, such as ammonium picrate, in the late 1890's. These new explosives could be fired from conventional cannon, and in combination with armor-piercing shells were an effective weapon versus armored warships. A dynamite gun was as expensive to construct as a 10 or 12-inch shore defense battery, but had a shorter range and was more expensive and complex to maintain. Moreover, the increasing range of ship-mounted weapons meant that an invading navy's guns would out range the dynamite gun and so could destroy it from a distance with impunity. As a result, dynamite guns were no longer useful and so were scrapped.
