We removed DFG because it was unhealthy for the game

These aren't even close to eachother.

???

There's nothing really wrong with Duskblade except it not being melee-only.

No, they removed Deathfire because there wasn't really a good reason to have it. Essentially, it was a "Win-More" item that you'd only buy if you were already snowballing in order to continue snowballing.

Every champion who used it didn't really need it. Veigar, Leblanc, Ahri, Annie, Diana, etc. already had enough damage without it, and it just made them even more frustrating to deal with.

On top of that, it didn't really have a trade off for anything. It's only purpose was to give you more damage, just like Deathcap, except DFG was cheaper. People would just buy whichever was more gold efficient, leaving nothing open for strategy.

Duskblade offers a good trade off for armor penetration instead of something like lifesteal. It's purpose is actually kind of the opposite of DFG, as it can help you come back if you're behind or get an edge if you're going even. It's not as valuable when you're ahead because you should already have enough damage to do your job, and should work on building items to help you adapt to the situations your put in.

The difference between the two items is that Duskblade is a strategy item with good opportunity costs built into it, while DFG was just a more efficient Deathcap. It's existence was just to keep a snowball rolling, and was therefore unhealthy for that reason.

+ = remove them both because they are unhealthy combined.