Your conclusion that Luke 14:28ff is about the cost of discipleship shows a lack of understanding of this passage.
The parable of checking if the nation of Israel has the means to be able to rebuild the second temple, which was levelled in 70 AD, places this parable squarely into the events that are happening in Jerusalem today. The word "tower" in this parable is a metaphor for the temple.
Matthew 21:33-36 and Mark 12:1-12 speaks of God building a tower/temple in the middle of His vineyard which he then leased out to his vinedressers.
Now in this parable in Luke 14:28ff we are told this
Luke 14:29-30: - 29 lest, after he has laid the foundation, and is not able to finish, all who see it begin to mock him, 30 saying, 'This man began to build and was not able to finish.'
NKJV
After Israel is not able to rebuild the temple, we see that the Kings of the earth gather at Armageddon for one last attempt to trample God's Sanctuary and His earth Hosts, but in verses 14:31-32 we see that there is a King, I assume Jesus, judging the kings of the earth at Armageddon. When Israel realises that this king is more powerful than they are, they immediately seek His terms of peace, and those terms are that they must forsake all to become His disciples
The chapter end with a warning that if their salt has lost its saltiness, then they would be thrown out onto the dung heap and rejected in keeping with the parable of the wicked vine dressers.
Yes, you are right about Luke 14:28ff touching on the cost of discipleship, but this passage also points to when God will begin redeeming Israel again.
It is my view that Luke 14:28ff will unfold in around 20 years from now.
You sight context as a reason to reject what I had posted, but you have only focus on one aspect of Luke 14:28ff and not considered how Luke 14:28ff fits into the End Time prophecies.
Shalom