I’ve been thinking about templars a lot, lately. Mainly about Tithian and Kalak. And the debate on whether Kalak 1) was even a champion, and 2) could grant spells to his templars, and 3) was using Sacha and Wyan to grant spells to his templars.
Tithian, for example, is NEVER shown to utilize templar magic. Or even mention it as a possibility. In fact, the only instance of a Tyrian templar actually using magic was a dwarf in one of the short stories accompanying an adventure, I think.
tl;dr I think that templars shouldn’t all just be clerical spell casters or warlock pacts or whatever. I think a templar’s TRUE strength is/has been/always should be the secular power they wield in their city-state. Those class abilities they had in 2e? Those were BEASTLY in the context of the setting.
Templars work best as a fairly-easy-to-enter prestige class, granting secular power and maybe the option of advancing spell casting or psionic ability. That’s how I would do it, and how I eventually plan on doing it myself.