You could hand-code in the missing feats, spells, class abilities and bonuses if you know how. Few do, fewer still want to bother with it. It's a
massive pain in the ass.
The so called "Plutonium" version of pirated material that could be added to Foundry was very much a point-in-time affair in early 2020 and all discussion of it was banned on any of Foundry's many discord channels. It was nigh impossible to keep it working through the many updates to Foundry over that time. The overwhelming majority don't bother and just pay WotC for the content and Mr. Primate to be able to use it. The original Plutonium version does not work any more, and no version of it I have ever seen has been working since the middle of 2020. Atropos went out of his way to ensure any updates to Foundry would break Plutonium in a bajillion ways. It was
very deliberate. To the best of my knowledge, the pirates largely gave up when Mr. Primate's importer offered a cheap solution for those who would buy the books on DDB.
If you want to get banned on a Foundry Discord channel, type the word "plutonium" in a channel and count the seconds to see how long it takes for a mod to arrive in your discussion area. In the summer of 2020, it was less than 10 seconds. It might be as many as 20 now, I don't really know. I have literally never seen it mentioned in Discord since the summer of 2020. [I am being facetious of course; please don't hassle a mod -- but yes, they will ban your ass for it.]
The overwhelming majority of 5e DMs that want to use Foundry VTT to run their 5e games pay to access the material on DDB as well as the Patreon to ensure it is importable. You cannot import a class feature, monster, spell, item, etc, that you do not own on DDB.
I am sure there are those who have limited incomes and just want to run the SRD version of the 5e rules. They don't have to spend money to do that. And they wouldn't otherwise be buying FG2 -- they would just use Roll20 for free with no addons. But for all others? They are paying for it to WotC at full retail via DDB. There is nothing "unethical" about that. Current subscribers for Mr Primate's patreon is about ~30,000 or so? I think that was the number when
@darjr and I were talking about it last month. Perhaps I am mistaken and that was the estimated monthly fee Mr. Primate was earning from his patreon.
Whatever the case, it indicates that there are a lot of people who are using DDB for Foundry VTT for 5e use. Those who are using it for PC import only use a free patreon shim by another author so that's more difficult to track. Whatever the case, it's a lot of people on DDB paying money to WotC to use their content in an online game of 5e.