Any evidence to support this assumption?
It's not an assumption, it's the result of thinking and reasoning.
Also if you think bitcoin needs to be modified you're the one that has to construct a valid point.
Doesn't the data already indicate that most people pay the minimum Tx fee despite most blocks being unfilled? (They have a choice of paying nothing and waiting a couple days)
That's because most clients force it on them.
Doesn't the data reflect that Tx fees are starting to cover the costs to secure the network
Lol no, compare the tx fees to the current block rewards.
Where is your evidence to suggest otherwise?
T'is in the blockchain baby.
Why would you assume people would pay 40 cents per tx fee with a full block vs 4 cents with an half empty block?
Because people aren't even paying 4 cents today.