Depends on your use case. First, AAVE is on ETH, and most arbitrage profits are on other chains. For example, there aren't a lot of flash loan providers on BSC (Binance Smart Chain) with deep liquidity, so everyone just uses flash swaps. The most profitable chain for arbs is BSC (binance smart chain). If you're using the loan for DEX arbitrage, then there is no point in using a third party loan provider like AAVE. You have to pay swap fees regardless, and a flash swap is "free" in the sense that you only pay the swap fees for the coins involved, and you must pay them whether you send the coins to the contract first, or if you borrow them and pay them back at the end.

So if you bring in outside money from a place like AAVE for a DEX arb, then whatever fees you are paying to AAVE are an extra, optional expense, since the swap fees must be paid regardless.

you can borrow from a DEX pool for a dex arb in a different pool or for the rest Of the complex transaction

I’m asking if borrowing from the dex pools itself is cheaper than borrowing from AAVE

The answer is yes, for DEX arbs, since you have to trade in the pools anyway and must pay the resulting fees.