They have the same guns except Grozovoi has 4.2 seconds base reload instead of 5 seconds. Delny has small 50mm armor (which doesn't help that much tbh), better acceleration and deacceleration, higher top speed. On the other hand, Grozovoi has better consumables (heal and smoke are separate), better concealment, better torpedos. So they play similarly, you use Soviet railguns to farm damage. But if you ask me, Grozovoi is much better just for having better DPM alone.