It took us 7 years to get lucky 7s on a slot machine.
It took us 7 years to realize how widely used 7 deadly sins was in fiction.
7 years ago, we defeated the 7 kin of Purgatory.
There were once 7 Warlords of the Sea. Not 7 years ago. I just felt like adding something that involved the number 7.
Hiro Mashima is a genius. I can see a connection. There's 7 letters in Mashima. 7 years of research and it's all paying off!!
The "second type of time skip" happened only in KHR! as far as I remember....and that turned out pretty horribly.To show how big of an impact on the world, the FT guild truly had. To show how the main cast will react in an new environment of the world they once knew so well. To show that no matter what time or era, the key to resolve most problems is the power of love and friendship (do not forget that this is a shounen). To show that even the greatest magic, has a price to pay. To throw a rock in to the river, thus changing it's course. Hmmmm, some other that I can't think about :p.
Actually, I'm not sure if it should be called a time skip, but rather a hibernation effect, as the time for the main cast didn't flow, but only for the outside world.
I guess Samurai Jack is the time of "time skip" where a character is flung into the future where Aku's evil is Law....but Fairy Tail doesn't deserve to be compared to Samurai Jack.
All the "changes" you're describing will have absolutely no resonance with the reader as Mashima never showed us any of those things about the Fairy Tail world before the 7 year jump. How does any of that matter to us when we knew nothing about those things before. We can't recognize a change if we only see the after and not the before. In that regard even KHR! had a lot more to show as having changed in 10 years than Fairy Tail in it's 7 year jump. Even in Bleach we could recognize change in characters over time. Every single one of Mashima's established character was frozen for 7 years. The only ones left to change are the members of Fairy Tail with 0 development time that no one cares about. He didn't use that time to change these characters into badasses...instead they got 7 years older and 7 times more pathetic. Considering we knew nothing about dark guilds, Zereff, etc. before the skip it DOES in fact make the jump pointless. There is nothing about the story that necessitated a time jump. He could've introduced those elements into the story 7 years earlier and it would've made just as much sense as having them jump in 7 years later.
I'd prefer they don't go back in time. This is a very unique time skip in which the whole world has changed but the main casts remain the same. I want to see how they cope with it. In other time skips, the world are surprised with the power-ups and growth of the characters. But in this one, the characters would be surprised with how the world changed when they weren't around.Spoiler!