Your logic is good, but timing is off. Ranchers will sell off excess herd until next year as feed becomes too expensive to make a profit. The rally in beef will start once the selling is over. I'm calling the rally for next spring. Buying COW now is fine but if you want a better price wait 6 months. Either way you are going to come out ahead by next summer.
I'm thinking about adding a position. The thinning appears to be real. It should be basic supply and demand. Less supply will increase the price and COW ETF units should increase with increased beef and pork prices.