Valve takes a 30% revenue cut from developers without providing much value in return for them and it's not like they're using it to do modern game development in any significant capacity. I don't think other competitors need to be held accountable for using underhanded methods if they are willing to put forward more equitable arrangements that are both attractive to themselves or other developers in other ways ...
I wouldn't say the services provided by Steam is not "much value." To me it's actually a lot of value, because otherwise many indie games wouldn't be able to sell to a world wide audience. This alone is worth the 30% IMHO.
As for other competitors, I'm not saying they shouldn't do marketing tricks. They already do, and I don't fault them for doing that (for example, I still have Epic games store installed, and I did purchase a few games on it). It's just that they still can't challenge Steam in any real capacity. My point is that this is really not Steam's fault, and it's not fair to curb Steam just because they are doing very well.