I am also having the same issue. Watched the above posted video (and others) online, have the replacement crank arm set and tools, the crank arm does not seem to want to budge. Did you end up finding a solution?
Hi there! My crank arm also de-threaded near the pedal, and as I was trying to replace it, it also started to de-thread at the base when I used the removal tool that Echelon sent me. I ended up enlisting the help of someone a bit stronger than me, who really jammed the removal tool (despite the de-threading) into the base of the crank arm. It took quite a bit of force and multiple tries because it was really de-threaded. Now, we can't remove the removal tool from the crank arm, but we were able to use it for its intended purpose and get the crank arm off. Now, the plan is to replace it with the new crank arm and pedals. Having someone hold the break down so the pedals don't move while you're working is also helpful.
It took a significant amount of elbow grease, but the key is to just try to get that removal screwed tool into the base of the crank arm as tightly as you can. It's possible, even if it's a bit de-threaded, you just might have difficulty removing the tool after the crank arm is off—okay if you're just going to be replacing it anyway.
I also found the above videos helpful for seeing how to use the removal tool.