Instead of adding a 2nd condensing unit, try adding spray foam and double glazed windows. I can keep my 2400 sqft Texas home ice cold with a small 3 ton system. There are similarly sized homes right down the street from me with 5+ tons of capacity across multiple condensing units.
The biggest problem with oversized cooling systems is latent heat removal. It's much better to have a slightly undersized system running constantly through the hottest part of the day than it is to have a very powerful system running with 50% duty cycle. It's also significantly better for system life (capacitors last much longer this way). During summer months, my hvac system cycles maybe one time between the hours of 10am and 10pm.
One thing I'll never understand is not having shutters, only curtains. I live in France, almost everyone has shutters. But in other countries it's often different. I lived in Thailand for a couple of years and had only curtains, so the sun would still get past the window pane, heat the curtain, and the AC would then have take this heat outside again. This seemed massively inefficient.
I thing the best compromise is using whatever traditional, passive means of cooling we can, and then AC as needed.
FWIW, it isn't either/or - we practice keeping the shades, curtains, and windows drawn when it is hot, open when it is cool.... and we have air conditioning. Best of both worlds.