That is definitely a weak point. I’ve seen some fibre glass or carbon skid plates but I don’t think they give enough protection. An extra layer of protection, like @Fat Rat suggests might be a solution.
Or keep rocks out of your life.
Smart fix would be to redesign the area that is weakest, as shown in the photos above. 2 plates that crack at the same exact point. They seem to be poured ejected molded aluminum. Ive seen the other plates and they do not seem that much better. Either that or just lower the replacement price so I can order a dozen and not break the bank. Trek seems very little interested in addressing this pour design. And contacting engineering seems impossible.
now I don't know what material Shimano's motor guards are made of, but they last damn well.
I have hit my engine cover several times and have never managed to crack it