Yes, and if you compare
Daivrat's text vs table you get another rules SNAFU because according to the text there is really no restriction against divine or psychic casters being Daivrats. Paizo's no stranger to fuck-ups like that tbh.
Stalwart Defender came out in Pathfinder Core and plain forgot to include the AC scaling ability in the table
or provide an explicit progression in the text (standard interpretation is that it scales at levels 1, 4, 7, 10) and they never ever fixed it. Just Paizo things. Paizo would like to send its assurances that it definitely playtests its products though.

You can also add it to spellcasters with
Pathfinder Savant,
Loremaster taking
Secret of Magical Discipline feats, just getting a plain scroll of it (or using Daivrat Spell-Fetch, Loremaster, or
Limited Wish) and using
Ring of Spell Knowledge II with UMD to avoid level penalties, or playing a
Samsaran race character with Mystic Past Life.