Did Vito think Barzini was more dangerous than Tattaglia?
No, he did not realize it was Barzini. He tells Tom "Idid not know UNTIL THIS DAY that it was Barzini all along." By "all along" I think he is saying it was Barzini who was really the power behind Sollozzo, and that Tattaglia was merely a front.
If you watch the meeting of all the Dons, you will see Tattaglia keep looking to Barzini to take the lead...and you see Barzini literally take over the meeting.
