Out of respect for your players, you should never change the play style, or feel of something in the course of balancing it. A grenade with no splash damage, a sniper rifle that doesn’t kill on a headshot, or a rocket launcher with no travel time are all going to confuse and frustrate players. Set by previous standards and experience, their expectations would be shattered. Once a product or feature is released, you should always aim to limit changes to rebalancing and not stray into redesigning.
Players are acutely aware of these changes too, even when the net change was positive. After the release of World of Warcraft: Cataclysm, Blizzard wanted to make an underpowered role within the game, feral druids, more viable in PVP. The initial attempt focusing on strong damage-over-time effects made feral druids too good. The following attempt to rebalance by lowering the damage-over-time in favor of direct burst, and lowered mobility caused an uproar from players. Feral druids became even stronger in the hands of skilled gamers, but played very differently. Few druid players seemed to support this change. Even after the results were seen, even some professional PVPers commented they’d prefer to stay underpowered and keep the old mechanics.
Even more than perfectly equal viability, equal effectiveness in unique niches should be the top priority of all balancing. It’s more fun, and many players prefer it this way. Traditional sniping is not particularly effective in recent Call of Duty games due to the level design. Yet within its own niche, nothing beats the accurate, long ranged stopping power of a sniper rifle. Its effectiveness in those rare situations keeps it unique, and no doubt appealing for some players.
At times even easily adjusted statistics, like damage, are central to defining its role. To avoid redesigning key elements of the game, you must identify those fundamental traits that cannot be changed.