The first part of your question is this feature request: MDL-49133 which is a good idea that no-one has got around to implementing.
To grade lots of responses efficiently, you should be using Quiz settings -> Results -> Manual grading screen (https://docs.moodle.org/en/Quiz_manual_grading_report)
To grade lots of responses efficiently, you should be using Quiz settings -> Results -> Manual grading screen (https://docs.moodle.org/en/Quiz_manual_grading_report)