Time to rant about the Alvarez arc and issues I had with it once more now that I've posted some spriggan redesigns. This might be long.
The largest reason Alvarez and anything following Tartaros fall so flat is because you can almost tell Mashima was checked out by that point. That his excitement for the series had dwindled.
I have this theory that Tartaros was meant to be the last arc of the series but there were still things unanswered meaning that he was forced into adding more on. Now I don't say this as someone who thinks tartaros should've been the end, but because none of the villains after this point have any weight to them when honestly they should. All the reveals feel like they're done to surprise the audience more than flesh out the story.
I'm someone who always hated the Irene as Erza's mom plot because we really didn't need it. It was a trend of "villain is a blood relative" twists mashima kept throwing in and by that point it was honestly more annoying than anything. Erza never had questions about her family. She was never focused on her past so introducing her mother felt so out of left field. Irene literally could've just been the person who was in charge of creating the tower of Heaven, maybe she was even the on who corrupted Jellal, and that would've done far more towards making me invested in a showdown between her and Erza than anything in canon.
In general the Spriggan 12 being set up as characters involved in the various arcs would've been so beneficial because it would've given readers actual reasons to be angry or upset. What if Invel was the one who created Deliora and consistently tried to create new ice demons to impress Zeref. What if Layla's death was originally believed to be an accident but as time goes on Lucy uncovers more deaths and incidents connected to her mother that eventually lead back to Brandish. The tartaros group answering to August, who is still devote to Zeref, giving us a more solid reason to believe him as a Wizard king and actual tangible terror at the thought of facing him if tartaros itself would bend to him.
And this isn't even getting into how all their designs seem so slapped together causing them to look more like mid level/filler villains than actual final arc antagonists. Compare them to any of the tartaros characters and it just instantly becomes so obvious which ones Mashima actually cared about. By that point he knew he just had to make the women scantily clad and his die hard fans would ignore everything else. Jacob Lessio is one of the first Spriggan I think of whenever I get angry over how rushed their designs are.
Even Zeref himself felt so disappointing as a villain because any hype built for him really peaked during the tartaros arc. I was sure he'd be the one to appear instead of Mard Geer. It felt like that's what tartaros was building to. But instead we someone new and Zeref was pushed back. We could talk about him torturing Mavis and how Mashima still wanted to paint things between them as romantic because heaven forbid Mavis actually be a human with emotions who gets mad and vengeful when she's hurt, but we'll move on.
Beyond just this, Alvarez kingdom could've been so very interesting to have in the background, mentioned every now and then off handedly by side characters or guild members when discussing the world around them. This idea of it always existing but just never seeming important to our leads who aren't thinking about the political side of things. Us getting Alvarez hints early on and Alvarez only increasing in importance would've been something for fans to hold onto and engage with.
Mashima really dropped the ball on the series following Tartaros from the gray villain arc that amounted to nothing, a 1 year time skip setting up Natsu and Lucy collecting guild members that ended with everyone miraculously back at the guild with no persuasion necessary, to his final antagonists carrying non of the weight he wanted because titles don't create fear. And it makes me so incredibly furious because all it would've taken was actual care and interest in his own creation.