That's a given on HackerNews, as there's only one frontpage. On Reddit that would be, users subscribed to the same subreddits would always see the same things on their frontpages. Same as users on YouTube subscribed to the same channels, users on Facebook who liked the same pages, and so on.
The real problem starts when the algorithm takes into account implicit user actions. E.g., two users are subscribed to the same channels, and both click on the same video. User A watches the whole video, user B leaves halfway through. If the algorithm takes that into account, now user A will see different suggestions than user B.
That's what gets the ball rolling into hyper specialized endless feeds which tend to push you into extremes, as small signals will end up being amplified without the user ever taking an explicit action other than clicking or not suggestions in the feed.
As long as every signal the algorithm takes into account is either a global state (user votes, total watch time, etc), or something the user explicitly and proactively has stated is their preference, I think that would be enough to curb most of the problems with algorithmic feeds.
Users could still manually configure feeds that provide hyper personalized, hyper specific, and hyper addictive content. But I bet the vast majority of users would never go beyond picking 1 specific sport, 2 personal hobbies and 3 genres of music they're interested in and calling it a day. Really, most would probably never even go that far. That's the reason platforms all converged on using those implicit signals, after all: they work much better than the user's explicit signals (if your ultimate goal is maximizing user retention/addiction, and you don't care at all about the collateral damage resulting from that).