I'd rather suspect being on GOG is an extra effort to provide their customers the option of choice and alternative to Steam (good thing), but that doesn't imply dealing with Steam / GOG from a business perspective is an equal or as swift process. Publishing on steam is a one-time deal with adding a new game, you push updates more or less as you wish and it's pushed by steam servers.
GOG may have other steps, I've no experience with them but I know you need to make a submission form for new games, maybe you need to for every update as well...? Considering it's been holidays and they're a third party company, it may take a longer time for them to get new updates out for <insert reason here>. They also rely more on their users to install and update on their own accord, as some may want at times, not being forced to update automatically. This is of course speculation on how the systems work, but slightly less speculation is that no, they do not consider GOG users second rate. In fact, the existence of GOG users is a completely optional extra effort that's been put in for the benefit of consumers, and to reach a wider market. There are some people who for what ever reason refuse to buy games on steam, or want to use other payment methods than credit card / paypal, and some people hunt the best deal even if it's a 10% discount.
I've never been a big fan of GOG and similar sites myself, much for that reason. Lazy me enjoys not having to go out of my way to stay tuned when updates are available so I can manually update it myself. There may be an occasional 10% to save on a game elsewhere than Steam, but that last 10% is definitely worth it for me for the sake of convenience 😊
