I totally agree with you. I never understood why people automatically assume all undead are forsaken, or like in another thread, people were assuming Kael’thas was a Horde character just because he was a blood elf.
Alonsus Faol never joined the Forsaken, he and Calia are Lordaerians who have strong ties with the Alliance. Faol in particular is the mentor of Uther and Turalyon, and an old friend of Greymane. In BtS he only interacts with the Alliance and he even held a mass in Stromgarde. He and Anduin resurrected Calia and when the burning of Teldrassil happened, he offered his help to the Alliance and went to Stormwind to heal the wounded night elves.
If Forsaken fans were worried that Calia was going to turn them into Alliance puppets, imagine Faol.