The easiest way to judge base stats is to just compare the LC Pokemon to each other and try and give out an average, or find some sort of median and see what Pokemon surpass the medians(s)
I talk about maths here a few times, but I'm too lazy to work anything out, so the numbers I give are just rough estimates or examples.
Let's look at Speed for an example. The minmon with the highest Speed Stat in LC is Voltorb, with 100, followed by Abra with 90. These are the upper limits of what a Pokemon could be, and no one can outspeed them without a boost or a Choice Scarf. The lowest speed is Munchlax with... 5, followed by Ferroseed with 10. These are the lowest, you'd have to be a pitiful Pokemon to go slower with any sort of reduction.
To not work out the actual average, we can sort of tell with these 2 extremes what sort of Pokemon would be considered reasonable. The middle speed tier is around 40-50, since these aren't too fast nor too slow. This means the standard for sweeping-ly fast Pokemon tend to be sort of 60+, since they can outspeed the majority of Pokemon.
The other way is simply by the threat system. Pokemon can be judged to be up to standard if they can hold their own against a categorized threat. For example, Pawniard is a big threat in LC right about now (actually, it was for a while now). Pokemon can be judged on a specific stat tier by finding out if they are capable of holding their own against a common threat, Pawnjard in this case. If it can keep up with these common threats, it has a godo tier, but if it's outclassed with these stats, it's bad.
So how to define a good BST? Either find out to see if it can keep up with common threats, or make sure it can outclass the average in some sort of way. There aren't any set standards I'm afraid, so this is all I can give you.