Aight. Soaking the soil, cutting the cup off, then placing the plug of dirt into a pre-dug hole in your new pot is the best way to go. Botany science incoming, don't have to read it, but you'll understand root systems better.
Picture #1. Roots. This plant is pretty well rootbound. Remember, the roots you can see "aren't doing anything" per se. There are hairs spiraling off everywhere.
Picture #2. Cross section of a root after the hairs have developed. Takes about a week for this to happen after the root has grown.
Picture #3. This picture looks pretty complex, it really isn't since you don't need to know any names, just the shape. You have 1 main root at first, the main root sprouts lateral roots, those lateral roots more lateral roots, so on and so forth.
Picture #4. This is a basic cross-section of any living vascular root. Could be an oak tree, could be from an alfalfa sprout, could be from MJ. Doesn't matter. The epidermis you see on there becomes root hairs. It completely encircles the root. (vascular rays are the plant's veins that transfer the goodies upwards. Did you know pH is actually a system of the frequency of hydrogen? Proper pH meshes because its the proper kind of hydrogen, when proton pumps in the root system moves cations across the cell membrane that aren't properly charged, it collides with improperly charged hydrogen in your plant and destroys what it hits. Crazy eh?)
Mary jane will bounce back from almost anything you throw at her as long as growth of anything is possible in the conditions you've provided. If you don't allow the roots to grow sideways (i.e. only cutting the bottom of your cup), they'll simply grow downward, hit bottom, then start growing upward, get too close to the top, then curve again. . . . but will take a week or two to do so. I will personally guarantee you that promoting excellent root growth will cause your plants to explode with growth above ground as well. Part of promoting good growth is a proper wet/dry cycle of watering. If your plant's soil is allowed to dry out between waterings, the roots go looking for water, makes them beefy. Roots pushing around trying to drink also oxygenates the soil and prevents root rot. If you use a proper wet dry cycle and have plenty of light, I promise your plant will grow .5-2 inches overnight after waterings in a good veg.
Wet/Dry watering - wait until your pot is light or your meter reads very low moisture, but before your plant begins to full on wilt, wilting is stress, dry conditions are not. After it is dried out, you want root ball saturation. Water slowly and steadily until water is running out the bottom of the pot into your drainage tray. Leave your plant for about 15 minutes to see if your plant will draw the water back up into the soil. If the tray is empty, water again until you have water in your drainage tray. After it remains for 15 minutes, dump it out and wait until it gets dry again. You can play with it a little, like watering twice, drying once, etc. Whatever gets the best results for the phenotype you're working on. I grew my monster by rotating 1 water, 1 dry - but I wasn't going for fast growth.