@Nox_Tenebris Looks like they were waiting for the big stuff because they plan to adapt arc 5 and arc 6, the last volume of arc 6 came out at the very end of December 2020. I don't think the wait is that big of a problem because they would have waited AGAIN for many years to do season 3 if they put out season 2 in 2017, so they would have had the season 1->season 2 problem AGAIN, but they simply couldn't just start on it.
Waiting is a HUGE problem because WAITING = LOSE YOUR STAFF.
Season 1 -> Season 2 is evidence of that, also you can't just start production as soon as a arc is done, you need to storyboard it all, you need to get the people to do that, then you need to get the people to animate it.
Yes, it finished the arc at the very end of 2017, christmas. It wasn't too long after that that it got its season announcement, but that wait because we didnt have arc 4 right off the bat made it so we lost a lot of good people from season 1 that just degraded the quality of the next, the good animators simply went to go work on MT instead.
Season 2 being ready in early 2018 is way too early, I think the fastest they could have done it is late 2019, they aren't going to start on anything until the arc is actually published and they need to actually read the arc too! But since they had to wait for season 2 WF took up other projects instead which is why we didn't get its production until 2019.
Going on to now, we waited some more, it seems KADOKAWA wanted to do arc 5 and 6 at the same time, unsure if this was always the plan, but wouldn't know. From a sales perspective this is the best option because of the ending, Arc 5 would have had to end after 4.5 volumes for no cliffhanger (WF's biggest enemy it seems, someone doesn't want a cliffhanger in the staff as seen from S1/S2 when there WAS cliffhangers in the arcs).
Season 4 should do arc 7+8, arc 8 will be done this year, so there should be no excuses for making us wait a while, it doesn't really matter though because s3 won't be done airing until somewhere in 2025, so probably won't have to wait too long after that for announcement will probably be announced at AJ 2026 or AJ 2027. White Fox has my prayers for adapting 12 - 14 volumes. They could lowkey pull an arc 3 for arc 7+8 and NO one will complain.
Another problem is that the story from arc 7 -> arc 8 is not done yet, but will maybe conclude in 2024, I hope KADOKAWA gets WF locked in for S4 now so they can just start on it immediately after s3, so we lose NOBODY, but unlikely. I hope they learn from their mistakes and don't lose staff this time. Probably won't be possible, but the sooner they start on it the better, need an announcement at AJ 2026 (assuming s3 finishes airing in 2025) to reassure they didn't screw up with that.
Regardless, everyone will enjoy Arc 5 and Arc 6, they are VERY strong arcs and if done properly will satisfy you for a WHILE. The ending of course will too! To be fair, if they wanted to you could TECHNICALLY halt the anime here for a while, but people will DEFINITELY want S4 after.