The issue of whether a diver is safer with a buddy or solo can only be answered by considering specific divers and situations. At the very least a narrow focus of conditions is necessary in order to derive useful suggestions.
Regarding new, learning, and unprepared divers:
Having a buddy who is cautious, prudent, with good common sense is a positive. Such a buddy can help catch simple beginner mistakes, provide a level of gas redundancy, and offer some assistance. Eliminating such a buddy shifts some of the risks no longer addressed and mitigated by the buddy to the individual diver who has not yet mastered basic fundamentals. Knowledge of what it truly means to be self reliant while solo, the steps that need to be implemented to maximize safety, along with the risks one is exposed to, are largely unknown to the beginning diver.
If we move across the spectrum to the negative buddy, we find one who is reckless with little apparent common sense. Following and relying on such increases the risk and complexity of the dive for a prudent diver, also. Somewhere in the middle range probably fall the majority, with its unknown quality, which could go either way, positive or negative. Caution should be exercised.
Safer with a buddy, good or bad, or solo? The result of the equation is not the most important aspect for the beginning, inexperienced, and unprepared diver. The most important aspect is to maximize safety by minimizing risk and complexity while learning to be a competent diver. This is done by diving with a competent professional, experienced and competent buddy, good sensible new buddy. All of which will usually result in a positive for beginner divers while they learn skills, knowledge, and gain the experience and competence that will allow them to safely expand their diving into the advanced diving disciplines in the future.