I wonder who actually bothered to read the OP. Instead, the first reaction is to defend GOG and try to shift blame towards either the OP or the developer. The OP clearly states the situation, and posts the reply of a support ticket where GOG staff replies and acknowledges its up to GOG now.

Let me quote it for the illiterate:

Hello,

We have access to newer builds for these games and if everything goes well then my colleague will upload necessary files in the upcoming days.

Regards,
Cypers,
GOG.com support

And if you read the OP, you will see that yes, the missing updates are game breaking.

I am following this development for way longer than the 3 weeks the OP mentioned. This issue with the Kingdom Rush games on GOG should have been fixed over an year ago, yet nobody wants to acknowledge the problem (initially the devs, but later, from the replies from GOG, it appear that GOG is not making the developers' lives any easier).

Good for you. GOG absolutely needs to make sure games are kept up to date within a reasonable time frame, and needs to be held to account if they don't. Especially the offline installers, which are the heart of DRM-free.

Unfortunately, GOG these days seems to be crawling with apologists, who are desperate to make any excuses they can for GOG's failings, as long as they can continue to get their cheap games.

GOG has no power to influence publishers, while ordinary users have enough power to contact publishers and simply ask them fix / upgrade their games.

Sounds legit, no doubt. (:

GOG representatives must contact publishers, especially when they already have multiple reports from customers about outdated or even broken games being sold on GOG. Customers don't receive salaries or any other benefits for contacting publishers, while there should definitely be a person (or even a department) on the GOG staff who must track and handle such cases.

Kingdom Rush is unplayable? I played it last month (except for some "bonus missions" and most of the silver and gold trophy badges. I didn't notice anything wrong with it. Of course, that was on Win 7. Is it a Win 10 problem?

Can't say anything about Frontiers. Played that one about two years ago (last update shows as 2018). There where no problems back then (Win 7).

aawwww, this is cute. You still think GOG has some concept of "shame".

GOG is not failing to disappoint these days.

Good luck on your quest, you have my sympathies.

I read the OP twice, before posting and both times it read as the Op had assumed that GoG had the files.

So
Sorry to the Op,
GoG are definitely in the wrong here and need to sort their act out

I would imagine they are just flooded with Covid and Christmas and Cyberpunk and other such things all at once and these relatively minor games are getting lost in the shuffle. Not defending them, it's complete B.S., but I'd guess that's the main reason for it. Never assume evil when simple incompetence and time budgets are the more likely reason.

If GOG wants to be a Steam competitor they should really make this stuff more streamlined, but then GOG can never be a real Steam competitor because of lack of DRM (and Steam's entrenched consumer base), so... weird middle-ground to try and walk I guess.

In my posting I only but a 50'50 blame on the developer and GOG but reading your post It seems like I was wrong and I stand corrected since you seem a lot more knowledgeable about the situation than I do.

Yes, as long as the store is aware a game is seriously out of date or broken on their store. I guess usually the stores are not aware, unless someone (usually the customers) inform them about the issue.

Even then, I am pretty sure stores like Steam (Valve), Epic and Humble Bundle don't actively contact the publishers even if they knew a game is buggy or out of date, unless there are lots of refunds issued.

I believe that e.g. Valve has a hands-off policy to their store and service, ie. they consider it mostly as a platform through which the publishers sell games to the customers, and Valve takes a cut from those purchases. They also expect that by default customers take their issues, which are related to the game itself and not the Steam service, directly to the publishers. If it is about a refund, then Valve acts as a middle-man as they handle money between the publisher and the customer.

"Streamlined" would probably mean that GOG should adopt a hands-off approach to the service, just like Valve to their Steam service, where Valve rarely acts as a middleman between the customers and the publishers, when it comes to communication, patching of the games etc.

To fully reach that though, I guess it might mean having to drop offline installers (because apparently they are still made my the GOG staff, and not the publishers), and some other things we expect from GOG.

Yeah, in an industry now completely built around the client style experience I don't envy them the position they've put themselves in. Not trying to preemptively defend them getting rid of offline installers, those are a big reason I shop here (especially for older games). Just saying it creates a lot of problems and I get that.

Offline installers are supposed to be generated automagically from the same files that make up the galaxy installation. There's no good reason why it should be a major burden for GOG staff.

https://docs.gog.com/offline-installers/

I applaud your intent, but I doubt it will be effective on these forums. GOG's too focused on social media, so the best way to shame them would be posting this on their twitter feed or facebook page. That way GOG will probably see it and may actually even give a shit since tons of other people will see it as well.