superficial
/ˌsuːpɚˈfɪʃəl/
adjective
lacking importance or significance
"His interest was superficial."
"While the initial report seemed promising, further investigation revealed its findings to be superficial and lacking in depth."
marginal
/ˈmɑɹdʒənəɫ/
adjective
having limited significance or importance
"The difference is marginal."
"The marginal improvement in her test scores was not enough to raise her grade to a passing level so she failed."
degrade
/dɪˈɡɹeɪd/
verb
to reduce the quality or effectiveness of something
"The signal will degrade."
"The video quality will degrade if you compress the file too much."