Do you know what variety you have? How about asking the neighbours for a root of theirs? And have you talked to them about how they grow theirs? I had a less than impressive plant once but got a new one and it made all the difference. Unfortunately I don't know the name of my current variety.

Also rhubarb loves moisture so not sure a raised bed is helpful.

And do you keep planting new roots? Rhubarb can grow for years undisturbed.

Talk to your neighbors. It grows like a weed in my climate.
I shove a spade into my three 'mother' plants every spring..last few weeks recently...and give away corms to friends that want them. I've done that for 15 yrs. Never mulched, fertilized, or watered. Other conditions might need some care.
But if you see it in a neighbors yard, they know best.
Mock their conditions. You might be over-tending it.

I've tried growing it 2 or 3 times. You're not supposed to pick it til the 2nd or 3rd year. Mine looks good the first year, puny the second year, and not usually more than ankle high the third and final year of it's life. I just chalk it up to being too far south for it to survive the summer heat. But somebody having a similar problem up north makes me think it's something I'm doing/not doing. I'm in southeast Missouri in zone 7.