I'm on a similar page to you but like other reacting here wouldn't jump as far as to say it's the same or no better than astrology. You asked somewhere what it's based off and why and people are just giving you their explainations. Basically it's just a psychological theory, based off a very crediable psychologist (carl jungs) speculations, which then got morphed into mbti by briggs and other briggs (can't remember their names, but mother and daughter basically) MBTI is just one version, the most famous and offical, of the different theories that arose from carl jungs original speculating. Personally I hate how much weight I've allowed to fall into these personality types and functions, but I do like the explaination of cognitive functions and I can relate to all functions. (as by the theory and human nature we all should since we all "supposedly" have all 8) I simply strongly related to the descriptions of INTP mainly function wise but also somewhat the descriptions you read online. Essientially, theres alot of horoscopes involved and ya some sounds are absolutute trash and straight bogus, however, there's alot of years of actual speculation and systemising involved, and whilst it's by no means followed any scientific reasoning (evidence besides observation of human behaviour) it's pretty fucking interesting in how well it checks out.

Conclusion: I'd say mbti or any other type explanation is by no means a sufficient way of understand the human psyche or personality, as life events, as well as simple general human adaptability and flexibility plays roles in peoples personalities. Surely there is much more we haven't yet discovered or deleved deep enough into as of yet as to how and why we function the way we do. MBTI and other function based theories are really only that, theories that give a more or less acceptable (or not acceptable, applies really to the individual experience) explanation or idea as to how we may work.

I just thought I'd also throw out, that regardless of whether it's scientific or not persay, it does have a nice set of reasoning and logic to it, which as somebody who speculates a lot is something I'm open to taking on board. You shouldn't dismiss something simply due to it not straight away checking out as a valid or solid idea. Always check it out yourself.