I think your point is the current Maxwell equations explain physics so well that if we change them to accommodate magnetic monopoles they would have to be worse. If I understand you right, it overlooks that we can add terms[0] to Maxwell's equations that don't affect predictions in a world free of magnetic monopoles:

∇⋅E = ρ(electric) / ϵ0

∇⋅B = μ0 * ρ(magnetic)

∇⨯E = -μ0 * J(magnetic) - ∂B/∂t

∇⨯B = μ0 * J(electric) + (μ0)(ϵ0)(∂E/∂t)

We could switch every physics textbook to using the above today, and the only difference would be setting ρ(magnetic) and J(magnetic) to zero when there are no monopoles in the problem.

[0] Griffiths Introduction to Electrodynamics 3E, Section 7.3.4