Unless things drastically changed with Shadowlands then people are exaggerating the negatives of the mythic LFG-tool, much like how they exaggerate that the social aspect of Classic is “dead”. The LFG-tool was actually a step back in terms of convenience; not only did you need to form groups yourself, you also had to once more walk to the dungeon entrance. In my experience it did promote some sociality. The retail LFG-tool has more in common with the design of Classic than the RDF-tool does, in spite of it being a newer feature.
If there’s one thing I find negative about the design of Mythics then it would be the timed challenge. The design is very unforgiving when it comes to wipes, and the timed challenge itself discourages written communication. But as far as grouping is concerned? I think the tool is great. I’ve never had to deal with gatekeeping personally. Not in Mythics, nor in Classic. Not saying those issues do not exist, but I do have the power to avoid such circles. And I gladly exercise that power.