Not even close. Semien grades as a plus in pretty much every defensive metric while Polanco grades well into the negatives in pretty much every defensive metric. Semien posted good numbers in 2018 and 2019 before dropping off in the 60 game season this past year, but I take any numbers from 2020 with a huge grain of salt. And just watching Semien play, he looks like a good shortstop whereas Polanco makes me cringe on a regular basis, especially that arm. One concern I have about Semien is length of contract and the fact he is 30 years old. While he looked very good as a 27-28 year old, that's far from a guarantee he will continue to look good as a 32 year old, especially at SS, where it feels the defensive decline happens quickly and without warning.