I suspect that thick mud fell onto the chain, then the mud would not pass through the derailleur cage, resulting in the derailleur essentially taking a circular path around the cassette and in this case deflecting into the spokes as well. A "stronger" derailleur wont prevent this if you get mud on the chain (or anything that prevents the chain from passing through the cage properly). As to the GRX derailleur I highly doubt it would work with your Claris 8 speed shifter. The Claris uses the "old" cable pull. Why would Shimano use cable that for their new gravel offerings when they have already changed for the 10 speed and above MTB and road groupsets. "Better" more expensive derailleurs usually just lighter and better made, which mean they will last longer under normal wear and tear. For the most part they will not resist abuse any better than lower rated goupsets. Just get another Claris derailleur.