For point 1, sure: Bitcoin does the same thing, and "blesses" a particular initial block as the starting point of the chain by hard-coding it into the client. No reason Tendermint wouldn't do the same thing.
I don't see how your point 2 solves anything, though; it's just failing to acknowledge the problem. Why is it reasonable for me to think that a supermajority of the nodes are honest? If validators are supposed to be computationally cheap to run, compared to bitcoin miners, then what stops an attacker from running lots of them to get a larger voting share?
Validators are expensive to run. You need to put down a large security deposit in order to be a validator, and being a cheating validator will cost you the entire deposit.
In the Bitcoin/cryptocurrency world, there's a rarely-voiced but firmly believed assumption that being annoying and expensive to attack makes you secure. So the response that you are saying doesn't solve anything is what is believed to be the solution.
I don't see how your point 2 solves anything, though; it's just failing to acknowledge the problem. Why is it reasonable for me to think that a supermajority of the nodes are honest? If validators are supposed to be computationally cheap to run, compared to bitcoin miners, then what stops an attacker from running lots of them to get a larger voting share?