Can DeFi apps build a moat? I.e. can they sustainably capture value over the long-term?

Between the code being open source and race-to-bottom dynamics with liquidity mining, most might say no

But "bluechips" like uniswap, maker and DyDx have remained relevant

How?

If it DeFi app acquires these properties, it's evolved into an autocatalytic system and is able to sustain itself into the future, escaping death (so long as governance doesn't ruin it)

While open source code and liquidity mining to no provide an edge in and of themselves, they do provide a means to securing advantage

Done well, they lead to a network effect, reputable brand, fanatic community and distributed contributor base