Also, once it became clear that either Tessio or Clemenza would betray Michael the Lampone regime was absolutely critical.
I don't believe it was "clear that either Tessio or Clemenza would betray Michael". Lampone with his powerful regime would know that he held a key position. If Paulie could betray Vito, why couldn't Rocco betray Michael? And if you're right about the covering of Michael's strength, why not letting Tessio build up a secret regime? If Tessio had known what was going on, he probably wouldn't have betrayed Michael.
