I have met with people like that online, they had to or wanted to study everything solo. I think one lived in some muslim country where everything was banned, a crime to even have books on such subjects
Sure, and I'm sympathetic to such people. You don't even need to have any particularly extreme story to have my sympathy. You could be living in a free country with three different temples within walking distance, but just be very skeptical of the hierarchical features of Tibetan Buddhism. I was one of those people myself for many years. But regardless of how sympathetic one's reasons for proceeding in this way may be, I still think it is very unlikely that you are going to get it right by trying to teach yourself from books. It just doesn't work like that. And I'm speaking somewhat from personal experience here too. I tried studying this stuff from books, and with considerable dedication, for several years, but once I started engaging in-person with the living tradition, it was all very different than I could have imagined, and my progress was dramatically improved for it.
And then there is the fact the guru is a core element of how the Vajrayana works as a system - not just someone to convey information about how to work the system.
And yes, there are a number of good teachers who are now teaching over the internet, to one extent or another.
There is a huge problem finding good teachers. These paths have a lot of crooks, looking to make easy buck, teaching you whatever for $$$.
Maybe I'm just lucky or I have a nose for who is sincere, but I have never once had a
bad teacher in this field, at least not in that way. The worst I can say is that some of them didn't really understand how to connect with Westerners and taught in a very formal way that didn't meet people where they are or succeed in conveying the underlying logic of the practices. In the lineages I work in, becoming a lama is a pretty heavily vetted matter.
Of course there
are bad teachers out there. But that just means that you need to be a little more discerning and keep looking for a good one. The occult world in general, taking this beyond just a discussion of the Vajrayana, has a lot of this attitude that there are bad actors out there and therefore its better to figure everything out on your own. I think this is deeply misguided, no different than saying that because bad dates and bad relationships happen, one should stay single and friendless their whole life. In reality, we need each other, and the deeper we want to go, the more important this is. In basically every culture in the world, it is understood that someone who wants to go far in the spiritual life needs a good guide and mentor.
I've also done a lot of study and experimentation on my own, as is the norm in western occultism, and some of those hard earned learnings are especially valuable in their own way. And in fact, even when working with a teacher, one is still always kind of figuring things out for yourself just in order to make the tradition your own. But my biggest strides and most of my paradigm shifts have come when working with teachers (again, not just in the Vajrayana).
I will say also that teachers are especially important when attempting to approach a tradition from another culture. There is just too much embodied understanding of radically different models of how to be and how to relate to situations that really require getting out of your own head and experiencing the way these things are lived.
I don't know much about the Buddhist stuff, except that the mantras give extremely good effects when properly unlocked.
I'm curious what you mean by "unlocked." How do you unlock a mantra?
Some people are just looking to experience strong effects, ecstasy, want physical results, get rid of depression & anxiety, unlock increased awareness, reach altered states, perhaps work with some deity. For this solo can be fine, although potentially a slippery slope.
Sure, and people are welcome to pursue all those goals, although some of them are a bit shallow and people will be selling themselves short if they stick with those goals long-term. Personally I have no problem with it if people want to use bits of Vajrayana flotsam to pursue their goals, but they shouldn't fall into thinking that they're actually practicing Vajrayana, or anything that particularly resembles it, just because they are using a Vajrayana mantra.