Given the difference in availability of jobs and the amount of code out there, unless you are working in startup world or on web dev, this would be a major red flag on a resume in a lot of cases. Even the use of the word "legacy" is a problem. Like, this isn't "legacy" you asshole, this is our companies highest revenue product with a decade of hard work behind it and we don't want somebody that is going to be constantly trying to shill rust when we hired you to help maintain an important C codebase that is part of the foundation of the business. We need you to get good at C, despite all its flaws and issues, not complain.
This kind of attitude only works in an exceedingly small part of the software world that just happens to be disproportionately represented on sites like HN. Elsewhere, it's not a good luck to be using words like "legacy" on a resume without a lot of explanatory text about why exactly it really was legacy and deserved a full rewrite.