No, the superlative degree is "most tirelessly."
The superlative degree of "old" is "oldest."
the superlative degree of much is most
The superlative degree of heavy is "heaviest."
The superlative degree of "broad" is "broadest."
The superlative degree of stout is stoutest.
"Fool" is a verb and a noun and, as such, does not have a superlative degree. The superlative degree of the adjective foolish is most foolish.
"Less" is the comparative degree of little. The superlative degree is least.
most often is the superlative degree for often
Thinnest is the superlative degree of thin.
Cleanest is the superlative degree of the word clean. Cleaner is the comparative degree
The superlative degree of "splendid" is "most splendid."