I'm sure we've been down this avenue before here, so forgive my repetition if that's the case.
About the most sensible comment about this debate that I've come across was from Bill Bryson's summary at the end of his book on this very topic who, paraphrasing from memory, basically said that all these weird and wonderful theories have been made by people who themselves obviously haven't a clue about play writing as it was conducted in the period, which was very often a very collaborative effort - with actors quite free to provide their own lines much as productions based on improv might do today - and with the troupe leader putting his name on the end product, as much for liability reasons as for those of artistic credit. However it is this very aspect to the process that exonerates Shakespeare and confirms, rather than removes, confidence in his authorship.
Individuals operating outside theatre companies did indeed compose entire self-penned plays, but even these weren't immune from the organic redaction process if a troupe took them on in production. In fact, Bryson concluded, whereas such redacted productions in published folio form are most often very easily spotted through obvious flaws, syntax switches, plot holes and discrepancies, along with various other aberrations and inconsistencies in their composition, Shakespeare's on the contrary actually stand up to such scrutiny incredibly well. From first play to last they exhibit remarkably uniform construction traits - from use of language to exposition techniques as well as many other aspects to how characters are portrayed, gradually developed within the plot, and (probably most importantly) an admirable avoidance of ex machina elements in plot resolutions. The writing process, with some parts patently written for certain players in the company, suggests a single author, with sufficient talent and sufficient power within the company to maintain huge consistency without recourse to contribution from members, and who maintained this authority and artistic consistency over some decades.
This leaves those who insist that he was not in fact the author of his own plays the rather weak hypothesis to prosecute that the entire oeuvre therefore is the work of just one other individual - one whose own writing career at least matched the attributed author in terms of length and productivity (not to mention undisputed quality), who had authority enough throughout the period to ensure minimal changes to each work from actors and the like despite having no input into that process once the original script had been handed over, who managed to successfully maintain this conspiracy and pretence from the late 1580s right up to the point of the publication of the First Folio, and all of this despite the highly public nature of the output's continual exposure to general scrutiny throughout the deceit, not to mention the rather more intense private scrutiny from the state itself as one would have expected went hand in hand with such royal patronage as the company enjoyed.
It's a hard case to argue - and from what I've read one that has never really been successfully achieved to conclusion. Every theory so far has contained a rather obvious flaw in that at least one important aspect to the playwright's life and career as far as we know it has to be discarded, discredited, or discounted as false, though for no reason other than to accommodate the proposed alternative which itself is normally predicated on rather singular speculation.