Sayle has explicitly stated that our sheild technology is generally poor and "nakedly inferior" to its Klingon equivalent (as are, relavently, our respective weapons technologies.) unlike in canon, we will not have a warp 8 fleet able to support this vessel in a conflict, as we cannot refit our existing fleet to the new engines. Additionally, whilst we have a larger torpedo armament and far greater manuverability, our phasers are barely more than half as powerful as the canon ones, ergo, it will take longer to destroy anything that isn't ripped up by torpedoes, requiring the ship endure more fire outside of ideal conditions. This being the case, it is therefore wise to invest in more powerful shields than the canonical Constitution design, as it is likely to endure more fire, more often, and more quickly than the canon design ever did.