USE CASE: How bad is this splash

[hitz]

So BG Dominaria sealed deck with 1 skittering surveyor.
Compare: 9 forest/5 swamp/2 island/2 plains (splashing for Taytova UG3, Cloudreader Sphinx U4, Blessed Light W4, Pegasus Courser 2W).

Do we have to "weight" value of a card for splash (i.e, Blessed Light ~= 1.8 cards of value)

e.g. this deck:

[hitz]

uh 3 on plains = 2.

[hitz]

assume replace white with 2 mediocre green cards.