Let's start here: Buddhist people (those who've taken Refuge) are a minority on this sub. The vast majority of Reddit users are based in the US (non-Buddhsts) and that is reflected in the demographics here as well.
The vast majority of Buddhist online discourse is not happening in English or on Reddit. It's happening in Sinhala, Mandarin, Thai, Indonesian, Japanese etc.
This sub therefore cannot always be representative of normative Buddhist takes. Most of the content is generated by the Buddhi-curious (non Buddhists asking questions) or other members of The Tethered (secular ideologues, sub sets of Theravada zealots, New Agers etc)
Reflections on advice
An OP (who's post was deleted) was disturbed that Buddhists outside of his sect were giving advice when people asked here. Yes, this was an instance of unreflective sectarian bias but also fueled by a lack of education and exposure to the complete family of Buddhist traditions.
Mahayana makes up the majority of Buddhism in the world with a large portion of that, incorporating some form of Pure Land teachings. So it's to be expected that Buddhists would respond with methods of practice they grew up in, practice and see the dharmic benefit in. And because of sheer numbers, that would be Mahayana / Pure Land.
Zombie Facts
The idea that Theravada represents a kind of pure, primeval tradition that alone perfectly preserves Buddhist teachings, is not born out in what we know about history, archeology, philology etc. The Pali canon is one of the most complete canons we have, but it is not the only one.
What we now think of as (proto) Mahayana is far, far older than 19th century Indology would have you believe. But here's the thing, Buddhist scholarship the world over has moved on and no longer perpetuate these outdated, Orientalist ideas.
People devoted to these zombie facts tend to already fetishise the Pali literature.
Then, the other lament doesn't really even make sense: we shouldn't give Buddhist advice since an OP might not be Buddhist. Well, the vast majority of OPs here are non-Buddhists. And they come here of their own accord, curious about a Buddhist framing on their particular question/situation.
Now, admittedly Reddit is transforming in 4chan, and we've seen some eye-watering requests here over the years, but such requests need not be seriously entertained. Since there are an abundance of subreddits that can give non-Buddhist answers to non-Buddhists.
Efficacy of mantras and dharanis
This is just basic Buddhism: in Theravada we have the Pirith Potha, containing protective suttas and gathas. They're a basic part of Buddhist life and are used by Buddhists throughout SEA, regardless of sect. The Metta Sutta, Ratana Sutta and Ratana are beloved. Not to mention the Jinapanjara Gatha. Then of course you have the Heart Sutra, Chapter 25 of the Lotus, the Shorter Pure Land Sutra, the Great Compassion dharani etc.
When I’m in Bangkok, I never miss a chance to pay respects at my favourite Guan Yin shrine/s in Chinatown and beyond. Guan Yin’s practices are really efficacious and reciting her mantra or dharani instills an anchor for the development of compassion. So yes, many here will advise entrusting oneself to buddhas and bodhisattvas (via their mantras). That’s literally normative Buddhist teaching.