Word or phrase for making something seem better by comparison
Solution 1:
The name for something that is used to make something else look different by comparison is a foil:
foil, noun. Anything that serves by contrast of colour or quality to adorn another thing or set it off to advantage.
The presence of a foil induces a cognitive bias known as a contrast effect.
I'm not aware of any terms that mean to create a foil or to induce a contrast effect.
Solution 2:
Watson is a perfect foil for Holmes because his relative obtuseness makes Holmes's deductions seem more brilliant.
[Britannica Online]
(emphasis mine.)