This is an exaggeration to be sure. And yes, oftentimes you can separate an artist from their art, and EotPT seems to be one of those cases.
That does not mean, in any way, that we should not criticize the man for what he apparently was as a person. Because very often, fandom goes beyond appreciating a particular piece of work and enters into idolizing its creator. That is clearly not appropriate for Barker at this juncture.
And I'm not saying that you're doing that, but some people do. And you're not the only one reading.
It's not much of one. EPT was the first licensed game. TSR licensed him to use adapted D&D OE mechanics. It was also pretty much the first game with prose about the setting. The first several national conventions where D&D was significant, EPT was there, as an advanced/alternate form of D&D, and with Gygax's blessings.
There are some implications that Barker may have been more influential than E. Gary Gygax Sr made out; the "Beyond Here Be Dragons" manuscript in his effects appears to be a late stage draft of OE D&D.
Tekumel/EPT are every bit as important as Metamorphosis Alpha, Tunnels and Trolls, RuneQuest, and Traveller. They were all commercial successes which proved that there was room in the RPG realm for games other than D&D, and for playstyles other than the "push your luck dungeoneering" (which is the style of play presented in the OE D&D rules, even if it wasn't what Gygax did at his tables)... Further, there were novels that brought people to EPT, at least later, and Phil's worldbuilding is comparable in scope to Tolkien, albeit with not as wide a fanbase. Phil's being an educator with a public wargaming hobby also brought a certain level of tolerance during the heyday of the Satanic Panic.
Phil not having done EPT wouldn't have killed the hobby, but it would have had some important effects. And I say this as someone who's never played Tekumel based games. Phil is a historical figure of note within FRPG-ing, and a spreader of the hobby. An influencer. His D&D spinoff, as well, expanded the audience for TTRPGs, because it did things slightly differently; RuneQuest, Traveller, MetA, T&T, and En Garde all did things differently, too. We don't, and can't, know where the tipping point was, but we can see that these games all did jointly push RPGs into more homes, hearts, and minds. 50 years on, and people are still playing Tekumel. And T&T. And RQ. And Traveller. And En Garde. And D&D.
By comparison, some other early games got no real traction... few have heard of Kaball, fewer still have read it, and fewer even have played/run it. Starships & Spacemen never got a big following; if FGU could have afforded the Trek License, it would likely be in that above list... but they couldn't, and it's a historical footnote. (Albeit one I have enjoyed off and on for decades.) There are a dozen other pre 1980 games that could have been important, but weren't, for various reasons.