I have had a rhubarb
It’s not ideal for Rhubarb to be grown in pots long term, especially if you want a thriving plant. When grown in pots the root structure and growth is limited and this affects the plants ability to develop nice thick stems.
My rhubarb has not performed
Rhubarb prefers nice, rich, organic, free draining soil in a spot that gets full sun. Firstly consider the age of the rhubarb plants in your garden - the average lifespan of rhubarb is 3-5 years.