so if a junior dev checks in 4k lines of crap code in the codebase, is that progress? And what do you call the more senior engineer that advises we make change

so if a junior dev checks in 4k lines of crap code in the codebase, is that progress? And what do you call the more senior engineer that advises we make changes carefully, and that there are subtle, important reasons why systems are working well today. Is that engineer a conservative?