I've seen a 2x4 put unwanted pressure on swingarms and wheel spokes.
The absolute worst cs sprocket I ever had to deal with was my 650 Versys. That thing was grossly over tightened at the factory.
I put the transmission in NEUTRAL then I press down hard on the rear brake then tie wire the brake lever down. This keeps all forces between the front and rear sprockets via the chain without impacts to the gears in the transmission.
In the Versys trouble, I used a 1/2 inch electric impact for a minute to no avail.
So I put my 1/2 inch breaker bar on with a four foot extension pipe. I practically lifted the whole back of the bike off the ground. I had the front strapped. The bike was vertical.
When the sprocket nut finally broke free it sounded like a gun shot. I actually thought I broke the countershaft itself.
Had I used a 2x4 I would have dented the Versys swingarm. It is light gauge aluminum. I torqued the new sprocket to factory spec and never had a problem. You can easily break a 90 ft/lb torqued nut with a 1/2 inch breaker bar alone using the method I described above.