That article's author says it's illegal. Neither the EPA nor a judge have made any judgments about Colossus generators being illegal (in fact, it doesn't sound like the EPA has made any enforcement actions at all, to date).

The article is about the EPA issuing a new rule (see the link behind "declared" in the article you linked to) closing the "nonroad engine" loophole, which the author of the article asserts makes those turbines illegal. The same new rule created a new subcategory allowing turbines for up to 24 months with streamlined compliance, and left a path open to EPA certification for turbines under Title II.

But the Colossus 1 turbines were already permitted by the time that article was published. At least 2/3 of the Colossus 2 turbines are permitted already too.

In the next month, there'll be a preliminary injunction hearing for the NAACP's lawsuit, but the DOD and DOJ both oppose the suit, so we'll see.

The companies doing this in Texas aren't even using that nonroad engine loophole - they're just getting Texas' minor permits. The EPA said in June that they're not going to create national rules, and instead defer to states. So you're seeing Virginia tighten regulation, and Texas loosen it.

So frankly, no, none of it is illegal. I think you're right that it should be, but that's a different problem, and not one you can help fix by claiming it is. If you want all this to be cleaner, go fix permitting for fixed clean energy generation, because it's a disaster.