Rhydon is an amazing pokemon actually, or really good at the least. It walls both zekrom and ho-oh, it does this better than rhyperior imo bc if you give it a spdef boosting nature it can also eat up draco meteors, which rhyperior cant. It also has much more overall bulk. It is a fantastic pokemon on stall as walling these pokemon is essential, and it provides stealth rocks as well. Only downside is you cant use something like rockeus to defog, but even on balance this is a decent choice if you're ho-oh and zek weak. Oh and it takes only 40% from a +6 gothitelle's psyshock and can roar it out (or if you run rest you cant but blergh) :D