First of all, I can see a problem here, Yes there's a lot of Menyoo/me maps that in general are pretty bad, also it floods the map category with a lot of dumbs maps, I'm supporting the idea to do a different category with maps, (DLC maps understood as "custom models with some complexity in their functioning like LODs,Traffic,Lights and behaviors, and the
"mainstream" Map Editors maps in his own category.
Next point is the amount of work of each method, In game method vs External method, both can be as good as the other or even better, here the problem isn't the tools by itself, because bad mods aren't fault of OpenIV authors or Map Editor author, is the people who uses those programs that make bad mods or quality mods, this depends of the usage of the tools by each user, this case is very similar with the image problem of Unity Engine that's a very pretty good game engine that suffers of shitty games create by the community, that manages to even public their games without any pinch of quality, also the tool itself , speaking of both tools (Map Editor /Menyoo , MME to ymap) are very good and easy to use which are very good to attract more people into modding with logic side effects such the mediocrity of the maps, but you aren't having this in mind, the style of doing this kind of maps is a lot more versatile and handy than the 3dsmax-ish maps, also is very similar to the level making of popular game engines like Unreal Engine 4 or Unity, all the models has to be made by hand and set placed in the world by the own designer hand in order to create a level and do this in modelling software are worse for some reasons like the performance,utility,etc.
Another point that you missed is the fact that this kind of programs can be used by ourselves to add some details to the custom maps that's always welcome and beneficiary in any sense, but you are being a hater of all the map editors which exists since a lot of time in a great variety of game engines, this is only a easier version, ingame that nearly everyone can use and upload their work to this page, i know that the great majority of them aren't very well crafted and it has bad quality but isn't a good idea to put someone to judge what mods deserves to be uploaded or not, I don't know any free mods page what do this, and Nexus Mods has a lot of mods of a large variety of games which also has his owns shit mods, but for good, you can skip it and good forward of the Top Mods and you will the best of the best for enhance your gaming experience.
Last thing, a message for all modders out here of any game, please, make sure that when you are doing your mod, keep in mind to do it as good as possible, don't upload it until the mod meets the wished objective and be good as it has to be. Happy Modding and let's make this game more alive than ever