You know it Felix !!
But seriously - I get that when someone puts allot of time and effort into something and then another wants to try and use it for nothing(that is wrong) But some of these tools are allot of money for someone who just want to use them as a non money making tool.. Maybe they could do what a program I've used before, (which I forgot the name of) was to get the user to sign an agreement licence - to pay a set price , if the tool gets used and there is money made.. Just a thought???
Whether you release something for free or for money, you are still going to be using the Spine runtimes to play back your animations within GMS - and this is really what you are paying for (in any language, not just GMS)
The only tool I know of that can use Spine files legally without owning Spine (ie. DragonBones Spine Export) is Defold, and that is because they wrote their own runtimes and don't use any code from the official Spine runtimes.
Instead of looking at it like "I have to pay for something when my game is free, and it's not fair", look at it as a monetary value for the time you spend using it.
Going to the cinema will cost around $20 including a drink and a hotdog / popcorn and lasts about 2hrs, which works out to around $10 per hour of entertainment.
Spine Essentials is $60 and you will spend way more than 6hrs using it, meaning the "value per hour" will work out to some tiny amount probably much less than $1 per hour - and you also gain skills learning how to use an industry standard tool as well as have the opportunity to earn money back from any games you create using Spine.
The Spine support in GMS isn't great but that is because of YYG, not Esoteric.
I don't usually white knight for software, but Spine is a great tool and is worth every penny, and I think the authors deserve to be paid for all the hard work they do in constantly improving the IDE and adding features, as well as keeping all the various runtimes upto date to support these features so what you see in Spine is what you get in your game.
Finally, $60 really isn't a big sum of money - save $5 a week and you'll have enough before you know it.
Use the Spine Trial whilst saving - you can import your work once you get a proper licence and by then you will be much more comfortable and proficient with it too.
Think of it as an investment in yourself, or in your hobby (coding) similar to buying a pair of football boots to play football, or trainers to go running, clothes for the gym or whatever other hobbies people pay to take part in.