I will never be able to move on from Alderamin (slight novel spoilers - Read the novels!)

Regarding Seven Spellblades, the anime does not promote the light novels properly.
The light novels and anime have different tones.
Light novel is very dark (even darker than Alderamin) while anime is more like a Harry Potter series.

There are many similar tropes between Alderamin and Seven Spellblades:
1) 6 major characters. All have character development.
2) Big sister trope among the six characters. In Alderamin, it was Yatori. In Seven Spellblades, it is Michela. Both being nobles and strongest among the group.
3) Multi personality disorder. In Alderamin, it was Haroma, being innocent but an enemy agent in reality. In Seven Spellblades, it is the protagonist Oliver, who looks gentle but in reality bloodthirsty.
4) Both protagonists having secret ulterior motives.
There are many more.

That's fair. In my opinion, I felt he was very justified in his decision, so I have never had problems with the ending.

Also I have heard some amazing things about Reign of the Seven Spellblades, but frankly, parts of the anime left me less than convinced to read the novels. I also heard the series falls off later on. Is that true? How does the anime compare to the novels as an adaptation in your opinion?

It's best to read from the start of Volume 1 because the anime changes the order of some events and skips vital information. What happens at the end of the last episode actually happens earlier in the light novels, but they wanted to make an epic cliffhanger so they changed the placement of it. The strategies and warfare in the light novels is a lot more enjoyable as it's more complex and detailed, so I highly recommend reading from the start. The anime doesn't mention some things that become important later on in the story, so you'll find yourself really confused if you don't.