No, that's not my complaint. I think the OP has a reasonable point, and I could see a case for an expanded list, but I'm taking about skill DCs.
Players aren't given any real information about their skills do. That's no way to translate a +7 Survival bonus into a list of abilities. We have the barest of guidance on seeing DCs for DMs, but there's no real difference between a DC 12 and DC 14 check, despite the significant range that is takes up out of the RNG.
By a "complete skill system" I mean one that can be leveraged by players to achieve specific results.
I highlighted a significant point of discussion here.
I'll begin with a brief response on the first part, however: the game needs 3 DC's (10, 15, and 20) to function described as easy, moderate, and difficult. That's not difficult to relate. The other main use is in opposed checks and that can be cinematically compared to the same easy, moderate, and difficult as well as being easy to use. If a DM wants slightly more difficult or extremely challenging then go outside those a little but it's still easy to relate.
Referring to a skill system as incomplete implies that there's something wrong with it or it's broken. This isn't the case. The system is working as intended where the DM determines checks and bonuses following presented guidelines as part of cooperative storytelling. When you say "can be leveraged by players" I read that as "we get to choose results instead of actions" and that's a part I disagree with.
The system is not incomplete. The system favors DM agency in determining results of player actions, which is how I believe the interaction should be.
The other thing that I would point out is a predetermined list of actions instead of examples limits the actions players might attempt more than a general guideline. Lists of actions and DC's can give an idea what a character can do but as those lists increase players and DM's can fall into the trap of "there's no rule for it so cannot do it" mentality. DM's and players either continue what we do now so the lists don't do that much or they don't do those other actions at all.
Tying that back to gathering information leads us to the fact that adding a bonus to the roll doesn't change how players see the numbers. Adding a skill proficiency doesn't tell anyone what they can or cannot do with the ability. The examples I cited earlier tells players something they might do. Adding a bonus is just adding a bonus because there isn't much point in creating rumors et al with massively high DC's in the first place. Giving the information to players should always be relatively easy because that's part of building the story and the goal isn't to make it harder to find a reason to go on an adventure.
Why would I, as a DM, invest time and effort into a more elaborate information system than what exists now when I want players to have that information in the first place? It's counter productive to do that, and it leads characters into thinking they might need another skill when most skill proficiencies are done as an ability check for most characters already due to typically having 4 or 5 skill proficiencies.
It's becomes bloat for some people who want a bigger number when high CHA convers the concept already.