IHMO, thats inaccurate. Here the generalization, is tester can only do 'user-end' point of (black-box)testing. There are jobs which requires tester to do 'white box'. This involves knowledge as well as doing repetitive works.

What I found was, most developers unwilling to do some basic testing for their modules. Even if you find bugs with logs & reproducible steps, they push their dev task to tester again like " can you perform 'git bisect' to find out the patch caused this bug"? or "Can you run 'tcpdump' from your reproducible steps?".etc.

worstcase is sometimes, software 'design flaws' (for example: arithmetic operation software missing division operations) are blamed on testing team for find it later.