For my first Stone Warden I avoided Stone Vines because I really didn't like the sound of the 50% movement penalty. I forgot how far I got, maybe 30.
I rolled a few more Stone Wardens and found out that the whole Earthen Vines branch is very effective except against about half the bosses. Besides those bosses, the vines did most of the killing! The 50% movement penalty still was annoying and I had to mindful of it, but it wasn't crippling.
My winner Stone Warden (my first and only winner, so far) was an experiment that went the distance. I went antimagic. With Eternal Guard prodigy, Wild Growth from antimagic and investing in saves, she was nigh unkillable when turtling (blocking). Here's a link to my winner (even though it didn't update to show that I won...) Rudalima
If I did it again, I think I would have not wasted the unlock of Harmony for Waters of Life because I ran into a number of shields with the effect. Similarly, unlocking Antimagic for Aura of Silence was minimally helpful since I had the Spellhunt Remnants already at Tier 5. Other than the vines, Shards and Eldritch Stone were quite helpful for dishing damage while turtled up.
Pro tip: You will be able to block damage based on the resistance types listed on your shields. The resistance percentage won't matter while blocking, it will block those damage types the same as if they were physical. So getting good shields that also have a variety of resistance types is very valuable.
Full disclosure: I've only played Normal difficulty.
I hope this helps.