This is the context: "I missed the diversity of church, it felt rather like a French-only church, or an under-21’s church may feel like—too homogeneous."
I want to use the word homogeneousitic, but I know it's not a word!
Yes, "too homogeneous" is appropriate.
Your example is one of the reasons many writers avoid adverbs (altogether). Since you are using "homogeneous" as a value judgement, not as a scientific description, the word "too" does not contribute meaningfully to the sentence. Consider:
"...church may feel homogeneous."
Meanwhile, as a scientific description, "too" also has no meaning. Something is either homogeneous, or it is not. Doesn't mean people won't understand what you mean, though!