"I sort of change my mind on it every day," Jake said about fighting his brother ... "One day I'll do it, the next day I'm like 'I don't think I should do that.'"

Remember, Jake called out Logan -- along with Conor McGregor and others -- following his KO victory over Nate Robinson on Saturday ... leading many to wonder, would he REALLY fight his own bro?

Now that he's had time to think about it, Jake says it's come down to this -- "I would just do it to prove people wrong."

Jake says he's sick of hearing everyone praise Logan as the superior fighter -- saying, "I'm like a 10-times better boxer."

"I've had 2 fights and I've been in the ring for a total of 7 minutes and I've knocked down my opponents 6 times in that 7 minutes."

Jake previously told us he's dead serious about pursuing a boxing career -- and wants to take on some bigger names.

Since then, athletes like ex-boxing champ Antonio Tarver and NHL star Evander Kane have called out Jake.

Bottom line ... he doesn't HAVE to fight Logan -- he's got options.