households filing jointly, regardless of standard deduction, usually pay the same marginal rate as income is pooled. so yes, that can be a disincentive to work relative to filing singly, depending on how the rates+brackets are set. if one will be discouraged from working, it’ll be the lower earner.

but if one wants to promote marriage, one can set an advantageous rate schedule for married households. it will still be true that the two earners would be taxed at the same marginal rate, but that marginal rate can be made lower than the same earner filing singly.