I think of your suggested idea of objective reviews and classifications quite often, but the problem ends up being discoverability. There have been a handful of sites that were highly useful by aggregating price and consumer sentiment/recommendations from Reddit. They get initial visibility and search traffic, then get penalized by Google. Froogle/Google shopping gets priority and is the only aggregator that Google really wants to include.

Look at defunct sites like Nextag that were moderately useful in the space-- they had free and paid placements. They were steadily growing search visibility until Google started pushing their own product (Froogle, free product listings in 2014ish) and Nextag suddenly "violated Google's policies" and lost 90%+ of their traffic rather quickly (probably 1MM daily visits to under 10k basically overnight). Google shopping technically offers "free product listing placement", hidden well below the ads-- likely as a defense to anti-trust on monopolization of that specific space.

Brickseek and CamelCamelCamel are the two most successful/long lived tools in the space-- and they grew their visibility from the now defunct but once huge deal site FatWallet and SlickDeals. Walled garden subreddits frequently disallow posting of specific tools, so it makes organic growth super challenging-- given that pretty much all commercial queries start with Google or Amazon.