I don't think there's any argument that Thomas is a Hall of Famer, but I don't think he would have made it in on the first ballot if it weren't for the PED thing, which helped him, possibly a lot. A lot of people who ordinarily would have been suspicious about Frank Thomas remembered him screaming
from the rooftops about the issue when nobody gave a shit and was all "dingers lol," he was submitting his own piss for tests to an independent lab as early as like 1995, and he was also the only player who willingly cooperated with the Mitchell Report against the advice of his own union
. In an era of "did he or didn't he," Thomas is probably the one guy who you can say, without a doubt, was not a steroid user.
He also avoided the usual discussions about being a one-dimensional slugger who was a horrible runner / defender and played the majority of his career at DH (as Scout
pointed out), which are discussions that I think would have pushed him off first ballot if they came up.