A couple points. First that depends on exactly what WOTC product you buy. Third Party publishers did receive money from Acquisition Incoprorated and Call of the Netherdeep as well as D&D novels and tons of WOTC-licensed content from DMs Guild.
DMsGuild content is by and large 3pp content. I understand that WotC gets a part of that, but that does not make it a WotC product.
Second the vast majority of 3rd party creators are making 5E adjacent material. If you don't buy Rime of the Frostmaiden for example out of protest, then you darn sure aren't going to buy the 3rd-party produced maps, monsters or magic books that are sold as companions to it.
I can use the maps for something else, I can use the monsters for something else, I can buy different 3pp content. None of these hurt 3pps, including the last one.
Your argument always seems to come down to ‘if you do not buy everything, you are hurting those you do not buy from’. No one buys everything, that is impossible. If I spend $50 a month and I still do so, even if it is on somewhat different 3pp products, then 3pps were not hurt by that.
I would guess those two examples represent a majority of the 3rd party published content in terms of sales volume and possibly in terms of revenue. So yes, you are hurting those 3rd party publishers if you refuse to buy WOTC content.
and I hurt those I do not buy from instead by buying these and not having infinite money, that is not much of an argument, see above.
I also doubt that they are the majority of 3pp content. I see the ranking and rough sales on DMsGuild…
Once you move past the published content you get to the fan content. Fewer people playing 5E and buying 5E material mean a smaller market for fan content, which means a smaller pot to go around and means less money for those creators.
and a bigger pot for other 3pps. This might be a bit of a shift in the market, but that is it
There is a reason this has been a golden age of D&D and fragmenting the fan base will undoubtedly hurt the community as a whole.
I am not sure about that, unless ‘the community’ is ‘D&D 5e’, I tend to see the community as larger than that