Onboarding groups of people together has efficiency and effectiveness advantages. Batch onboarding makes better use of the time of all those involved in onboarding because there is less repetition, better benchmarking, healthy competition and natural cohorts that can help and push each other along the way.
So, say no when something should be done not ever, not now, not by me, not alone, not live, not again, not well. This frees you up to spend your time on the thing that you should do NOW (Next, Once, Well). Onboarding is a crucible of leadership for all involved. Batching new hires may help you and your team apply the right resources to onboarding at the right time, once, well.