The relevance of translation and law degrees as pathways to professional legal translation is the subject of persistent debate, but there is limited research on the relationship between legal translators' backgrounds and competence levels in practice. This study compares the revision performance of several groups of institutional translators (44 in total) according to their academic backgrounds (legal translation specialisation, translation degrees with no legal specialisation, law degrees or other degrees) and legal translation experience (more or less than three years). The scores of justified, missing and over-corrections, among other indicators, corroborate the crucial impact of legal translation specialisation and subject-matter knowledge in ensuring legal translation quality, while experience can serve to partially fill certain training deficits. Qualified translators with a legal specialisation stood out as the most efficient revisers, followed by law graduates, translation graduates without a legal specialisation and other translators. A subsequent holistic assessment of the revised target text yielded results globally in line with the revision scores, as well as mixed perceptions of the target text as potential machine output. The findings support the added value of legal translator training, and are of relevance for translator recruitment and workflow management. They also challenge the rationale behind ISO 20771:2020 qualification requirements.