The gemara on amud alef discusses the process of miluy v'iruy confirming that it would work to kasher from yayin nesech even for earthenware. Yet, the gemara on amud beis says that "kinsa" which would be a light burning on the inside of the vessel would not be sufficient to kasher for yayin nesech. Rashi (d.h. v'hilchisa) makes a logical assumption that something heated by fire cannot be better than fire itself, therefore if "kinsa" doesn't work, neither would hag'ola with hot water. The obvious conclusion is that miluy v'iruy would prove to be a better form of kashering (at least for items that absorbed without heat) than hag'ola. The chidushei anshei sheim (printed on the pages of rif) confirms that this is indeed the opinion of rashi, which is against the seifer ha'terumos who says that whenever miluy v'iruy works, hag'ola would certainly work. Tosafos in the name of Rabbeinu Tam also seems to assume that even a minimal hag'ola that would not normally work for issurim (such as pouring in hot water and swooshing it around the barrel) would work here. This would be consistent with the sefer ha'terumos that even a minimal hag'ola is better than miluy v'iryu, so a proper hag'ola would certainly work whenever we allow miluy vi'ruy - unlike rashi.
I would like to offer another interpretation of rashi, so that rashi would be consistent with the sefer haterumos and Rabbeinu Tam. The sefer toras habyais (re'ah) writes that there is a big difference between kashering through hag'ola and kashering through libun. Libun burns the issur in its place whereas hag'ola is "maflit" - extracts the issur. Rashi's kal v'chomer that if "kinsa" doesn't work, certainly hag'ola wouldn't work is true from the perspective of burning out the issur. Since the actual fire cannot destroy the issur, a product of fire i.e. hot water certainly cannot destroy the issur. This is all within the realm of "libun", meaning when hot water is going to use the mechanism of kinsa which rashi holds is the only mechanism possible by earthenware (because hag'ola doesn't work for earthenware as the gemara says in pesachim). Rashi never entertains actual hag'ola extracting issur because it doesn't work by earthenware. However, miluy v'iruy which allows for 72 hours of diluting will be a better form of extraction of issur than hag'ola for earthenware since hag'ola doesn't work remove the issur. But, for other materials such as metal, where hot water can work as hag'ola and not just as a way of destroying the issur, rashi may very well agree with the sefer haterumos and tosafos that whenever miluy v'iruy would work, hag'ola would certainly work.