BDS would be easier for mainland students. It emphasize more on clinical and surgical training compared to MBBS.
Having said that, the 6 students chose MBBS should be confidence in their English proficiency.
Unless the quota is set down to each programme, the high performance mainland students will push the local students down the pecking order.
Universities always prefer applicants with high academic scores and the admission process should be merit based. More quality non local applicants can only push the local students to less preferable programmes if the quota is not set appropriately.