I haven't tried Stellaris, but I've heard complaints that it suffers from a "don't know how well you're doing" problem, in that you can be many hours into a game before you encounter other aliens and immediately realize that you're so far behind that your eventual defeat is inevitable.

Have you encountered that problem and/or do you know if it has been addressed?

Stellaris suffers from many things. Civ (and all other historically inspired games) draw a lot from the relatable content. If Ghandi threatens Cesar with nuclear weapons, it may be absurd, but we relate to this absurdity in ways that we don't relate to [randomized species A] threatens [randomized species B] with [deadly thing that is supposed to be more deadly than some other deadly things].

Stellaris is trying to be generic (the Stellaris world could be the background for almost any interstellar epic, it's full of little cameo references to every sci-fi classic the authors could think of), where Alpha Centauri went to great lengths filling the canvas, in one specific way.

Yeah it does happen, but that's part of the fun. It's not a 'set up a game, put X hours in and win' situation.

If you do encounter that in a game just do what you'd perhaps do 'in real life': try and be friends with them and not tempt them to anihalate you until you're strong enough to defend yourself. That might mean giving them resources, or not taking stars near their borders. And obviously up your ship building capacity and start investing more resources there.

That's an important point. Stellaris is intended to not be a defined, balanced race from planet to galactic empire, but more a "biography simulator" for a space-faring civilization: you may have older siblings and they will always be older than you. An important conceptual step away from the "Empire" roots that will be much easier to grasp for those who have been exposed to other Paradox titles like CK2 (where a single paythrough might go from count to emperor and back to count again, and then make the jump to a completely different religious group where a similar story unfolds under different rules) or EU4.

But Stellaris fails to pull it off. There are a few sleeping giants which, after learning the hard way, you'll just ignore until you are ready to take them on. When you have mastered those pitfalls (and that isn't hard) you are back to the single-minded race for empire, with no interesting goals for those left behind due to some early blunder which stalled the resource throughput growth rate for a while.

Hm, The best answer as I see it is that the game allows you to set both the size of the galaxy (map) and the number of civilizations in it (competitors). If you are concerned with not seeing competition soon enough, you can always tweak those settings to ensure you do, although I personally have never had that issue.