Why do swaps for different token pairs on uniswap have different gas fees (using Metamask)?

Question

For example, If I try to swap USDT to PBX, the estimated gas fee (METAMASK) is $700. But if I try to swap the same amount of USDT to ETH, the estimated gas fee is only $300. I understand that Gas fees are based on the complexity of the transaction as well as how congested the network is. But assuming I tried to execute both of them at the same time (therefore congestion would be the same) could the transactions I mentioned really differ that much in complexity to justify the cost difference?

Also, does it cost more gas to use a tool like dextools.io than the actual uniswap application?

Answer 1

I understand that Gas fees are based on the complexity of the transaction as well as how congested the network is.

This is true, but your price discrepancy is most certainly due to order routing and splitting.

Metamask swaps, ParaSwap or similar services will split your order across several providers in order to fulfill your swap. When a split is necessary, more gas needs to be paid because more liquidity providers are involved, which can greatly increase your transaction gas fee.

Answer 2

Different tokens have different transfer gas costs, moreover even token balance is important. For example receiving tokens ok empty balance would cost you 15k gas more in average.