Yes. Yes it is. Steam built the online games distribution market from basically nothing to where it is today. They helped usher in the indie game explosion, and gave players unprecedented tools for finding and assessing games. Not to mention the normalization of high-discount sales.
Oh yeah, and also Valve went ahead and made Linux gaming a more realistic proposition than it has ever been in history.
But that doesn't mean that steam today is the best experience for gaming, and I would probably go so far as to argue that their hold on gaming is harmful to the industry, the largest issue imo being their large take of sales.
Steam is where it is today because it first earned, and then kept, gamer trust. All the anti-Valve propaganda out there the past few years doesn't change that.
If you're buying the game to play with someone, you buy it on whatever platform the other person has it on.
Otherwise, you look at whatever platform you spend the most time on. If it's available there and the price is "reasonable" for you, then you buy it there. End of story. I don't believe that most people actively search out a new platform.
Otherwise, if it's not available or you think you can get it for lower cost elsewhere, then you go to the next store you think is likely to have it or have it cheaper.
Given that framework, it doesn't really matter how good a platform is for a consumer outside of being able to buy a certain game. The main factors for that platform are:
1. How many people are on it. and 2. How wide the selection on the platform is.
So I would argue that not only does the platform compete for users on 1 (which I've argued is mostly based on 2 and pricing), but also for developers on 2. I think steam's behavior with their features is mostly oriented towards making the platform attractive to developers, and Epic is offering exclusives and $$$ to draw developers in.
As to whether Epic's exclusives are good for that gaming community, you can argue that they will allow for an ecosystem of epic subsidized developers, and lead to more competition from steam for holding developers.
Also, for a consumer there's a big convenience advantage to having a single store - from UX perspective (but probably not from the wider market leverage perspective, tragedy of commons yadda yadda) I'd very, very much prefer using a single service that's good enough to having to use three or more separate places that each individually are somehow better but each doesn't carry all the content that I want. The same applies to most other media - movies/shows, music, books.
IMHO the only way to get competitiveness would be to ensure that exclusivity deals are impossible/illegal, so that you might have multiple services each providing all content but competing on other qualities.
I think some things they do well are (which are admittedly important things):
* reliability * security * fast downloads * consistent achievements between games
But I think they're lagging others (mainly discord) in chat and social. Their voice quality is comparatively horrible. They don't really have a good space for a group to have a server like discord does, which really helps with cohesion. So while I definitely don't think epic is killing it in any of these areas, I don't think steam has that much going for it outside their core competency.