Alright so, I have a lot to say on this, so bear with me! The short answer of it is... maybe? I'm leaning no, though.
I suppose there's validity to the perspective of the Shiny Charm decreasing value, but even without the Shiny Charm, you can SOS Chain for shinies fine without it and make some decent progress assuming you have the patience. In general, SM made it super easy (or at least, significantly easier than in past titles) to encounter shinies, thanks to the introduction of the SOS Chaining method as well as the the ease of obtaining the Shiny Charm, since you only need to complex the regional dex to obtain it.
That all said, it's not like you're near-guaranteed to encounter shinies every battle or anything like that. I don't remember the exact numbers off the top of my head, but even with the Shiny Charm + SOS Chaining, you'd still have to work quite a bit to get a shiny. Of course, luck can play into this, as well. The same can go for the Masuda Method in which case I believe the Shiny Charm has an effect on that too, but be prepared for the outcome of probably hatching hundreds of eggs for that shiny which will be a tedious task, to say the least.
This is all to say that while it is easier to encounter shinies than in past generations, shinies themselves aren't really less valuable, I don't think.