From my own experience (very personnal and subjective one) you can't be profitable until you acquire enough routed volume. It means to have at least 2 or 3 BTC capacity, 50 big channels of a minimum 5 millions sats each, and enough good peers... And even with that you can expect few hundred or thousands sats in net positive at the end of the month, if you managed your liquidity well.

I think you have to manage your liquidity by avoiding swaps and rebalancing, just playing with the fees. If you are skilled enough you can automatized the changes in your fees.

To conclude I would say that the only way to be profitable is to be one the biggest node or by selling Lightning related services through your node, but no routing only.