Network Links are something that I now just rediscovered for myself in Hyrule Warriors: Legends. One the Wii U I stopped using them at some point and on the 3DS I had both Network and StreetPass Links turned off the entire time, because they tend to get in the way. Sometimes you just want to do a certain mission, but it's blocked by a sturdy Level 99 Network Link, while it doesn't offer any worthwhile reward.
But now in my grinding phase, where I have all the best weapon tiers unlocked, they seem to be the best way of getting good weapons of the highest tiers right now. I had the same impression, when the Wii U game originally came out - early on it seemed like the best way of getting good tier 3 weapons. The Network Links offer a similar result to the Zelda amiibo, where you are guaranteed to get the highest available tiers of weapons for Link, Toon Link, Zelda, Ganondorf, Sheik and both Midnas, with three stars minimum. However, it doesn't seem like you can get eight slots with these methods, so you have to settle for a 5 star, 7 slot weapon at best.
But since I personally don't care much for Duel or Special Skills, I can settle for 7 slots. It's better than farming on the same missions over and over again, where you have to be really lucky to find a weapon of tiers 4 or even 4+. You need a Weapon Rank II or III mixture, but then getting eight slots is very lucky as well. So, finding a perfect weapon of tier 4+ with 5 stars and 8 slots is too rare for my taste. And this is why I'm back to the beginning, where Network Links seem to be the best solution. (I still would like the abilities to buy stars and slots in the Smithy, because then you could just buy that last slot, even if it probably was very expansive.)
Farming Network Links can also be entertaining for a while, because the Network Link Adventure Battles are somewhat randomly generated based on certain templates. In general Network Links of the same level seem to give the same scenario, only the officers might have been swapped. But these templates seem to be entirely different on each Adventure Map, so there's some variety.
In general you want the Network Links' levels to be as low as possible, because the level doesn't seem to have any effect on the reward. And the higher level Network Links will simply take longer to finish. The problem is that the level is based on your highest Level character in the game. So, if you have someone on Level 150 already, all your Network Links will be on 150 and annoy people. And therefore the randomly offered Network Links tend to get quite high.
Luckily I have two people on my friend list, who just started the game. And Network Links from friends will be favored by the game, so each day I'm getting at least two low level Network Links on every Adventure Map. And while the Network Links of the same friend all have the same level, the mission type is completely different on every map. So, it doesn't get too boring and it's more than enough for my daily grinding sessions.
The Adventure Maps also all seem to keep their own quirks for the Network Link battles. The first Adventure Map usually has a recommended element and lots of enemies weak to that particular element. The Master Quest and Master Wind Waker Map keep their Master Rules. And the Koholint Map occasionally lets you chose a 2nd character. You can even find fairy food, if the underlying battle has fairy food available.
With this you can also notice that each Adventure Map has a different base difficulty. I keep playing Network Links from the same guy on the same level, but the difficulty increases on a noticeable scale with every map. Originally on the Wii U I even had the theory that every Adventure Map followed one the four base difficulties: Easy, Normal, Hard and Hero, where the Twilight Map probably was Hero. But it's not that simple, because on the Twilight Map enemies have a high defense, which can be countered by elemental weakness, which doesn't work as well in Hero Mode. And then the Termina Map might have "Hero" difficulty as well, but with much lower levels for every mission. It would be nice to see the recommended level for every square, because then it would be easier to judge the difficulties of the individual maps and missions. Some transparency with the difficulty in Adventure Mode would be nice, so it's not just always trial and error. Maybe in the next game...