We built out an extensive comparison tool (as a vendor) and it was honestly a pain in the ass with little payoff.
The issue always came down to data providers and being able to accurately assess what is a base feature, a nice to have, premium, etc.
For example, our data provider would like "automatic windows" in the same category as "rain detecting wiper blades" or "lane keep assist".
Further to that, every manufacturer has their own name for things and the provider gives us that name, without a more generic translation.
If there was a great data provider that categorized things already it would be immensely helpful, otherwise it really relies on some form of manual categorization to determine what is a valuable feature and what is not. I find this especially important when looking at all the self-driving-adjacent features in cars now. I need to know if the car will stay between the lines, adapt cruise control speed, etc. Most of the time I see this information, it's a bullet point in an endless list of features that every car has.
If I was a new car dealer, I would fix this in-house for my own manufacturer details and offer a kickass compare tool because I do feel it has immense value when done correctly.