Melee nerf reduces player choice. This is the conclusion I have reached after a number of considerations.
1. Melee weapon is short range with higher potential damage.
2. Ranged weapon is long range with lower potential damage.
3. Ranged weapons is always better in cases where enemy can be one/two-shot by Ranged weapons. Let's call this "Range Optimized Levels"
4. When ranged weapon damage is insufficient on steelpath and long endurance runs,, melee takes over. Let's call this "Melee Optimized Levels"
5. Each player has a different level range of when enemy levels switch from Range Optimized to Melee Optimized.
6. Warframe is a game with infinite enemy level scaling but no infinite rewards scaling. Therefore it doesn't really matter what enemy levels players are able to reach, beyond bragging rights.
For example, a starting player may find that Range Optimized Levels for him is between 1 to 60 level enemies,.
For example, a MR20+ player may find that Range Optimized Levels for him is between 1 to 100 level enemies.
For example, a fully maxed player with rivens and latest meta weapon may find that Range Optimized Levels for him is between 1 to 150 level enemies.
Now let's assume, (1) and (2) remains true after the gun buff and melee nerf, then the level range of Range Optimized Levels shifts to the right for everyone. This is fine but do not really make much change to the existing meta. Players will still use Ranged weapons until they can't.
Now if we assumed (1) is no longer true, meaning that Melee weapon is short range with lower potential damage and Ranged weapon is long range with higher potential damage. Then every level becomes Range Optimized Levels, effectively deleting melee weapons as a weapon class.
Based on the above, the outcome is either neutral, or bad.