Is this statement true?
Optimization TSP problems are known to be NP-hard, as we do not have a minimum cost to compare against, and in order to verify a solution is optimal, we need to iterate across the solution space.
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This statement seems quite vague and confused.
NP-hardness is precisely defined, and you shouldn't loosely say "optimization TSP problems" because it doesn't specify the problem(s). In fact, it is not uncommon that seemingly small changes in a problem lead to different complexities.
Further, because NP-hardness is precisely defined, a problem is not NP-hard because "we do not have a minimum cost to compare against", but because for every problem $X$ in NP there is a polynomial-time reduction to the problem in question - by definition.
Finally, the expression "... to verify a solution is optimal, we need to iterate across the solution space" should be fleshed out more precisely. If the claim is "to verify a solution is optimal, we must inspect every possible solution of the search space", this is wrong.