Since Greg Maxwell is the posterchild for integrity, and has never tried to mislead anyone in his life, it is safe to take his word for it without any evidence. /s
He's certainly more trustworthy than the likes of Ver, Jihan,
Both Roger Ver and Jihan Wu stand to each lose tens of millions, if not hundreds of millions of dollars if Bitcoin is harmed over the long run. Greg Maxwell on the other hand stands to profit handsomely if Bitcoin becomes a settlement layer, regardless of the damage done to Bitcoin as a result of this. The financial incentives of Ver and Wu are clearly aligned with that of Bitcoin while those of Maxwell are not.
Greg Maxwell also has a fairly long history of dishonesty, deception and the use of sockpuppets to further his agenda. He was even caught vandalizing wikipedia pages maliciously in 2006 by his peers, and once he was temporarily banned for this, he used sockpuppets to do the same.