It's unclear whether the question asked is about the process of research or the process of publishing. If the latter, which may be suggested by the phrasing "chances of getting published", I feel like this question betrays some wrong thinking regarding authorship.
For a given work, everyone who contributed as an author should be credited as one, and no one should be added as an author who didn't contribute as one. No modifications to this should be made in either direction to game the publishing process.
For the process of research part, though, I do think it's more challenging to publish as a single author. Doing all the work yourself may not be as efficient as collaborating with others and combining your strengths, and you are more likely to miss key implications or weaknesses in the work. Most importantly, you lack the collaborative back and forth process that shapes your ideas and thinking.