I don't understand the relation you're alluding to between halvings and transaction fees. As far as I'm concerned, they're entirely unrelated. It's true that both big spikes in transaction fees happened to occur four years apart and in the vicinity of halvings, but that could just be coincidental -- if it's not, I don't understand the mechanism that would cause it.
In any case, neither spike was particularly long-lasting, and even if they were sustained at their peak, neither would make up for the mining incentive lost in the next halving.