What modern levers with return spring would be recommended, these would need to not be brake/shifter levers as I will be using down tube shifters and would prefer non-areo, but areo will do too.

So it's a combination of a stiff spring, lack of leverage in the single pivot design and no return spring in the brake lever? More things than I had originally thought, but all make sense, as there's no comparison in hand effort to brake between my Record brake/shifter levers with dual pivot brakes and the single pivot brake with the same brake/shifter levers.