Unfortunately, you're not alone in having these misconceptions about US regulations or forex broker reviews.
It's important to understand that unless a forex broker is brand new or has a small client base, you're likely to find some negative reviews simply due to the percentages. That said, regulation by a reputable financial authority can go a long way to addressing a lot of the concerns you may have.
For example, the CFTC and NFA set the requirements a broker must meet in order to offer forex trading to US residents. Though not an exhaustive list, this membership application will give you an idea of some of those requirements: https://www.nfa.futures.org/registration-membership/who-has-to-register/rfed-applicants-compliance-requirements.html
Particularly noteworthy are the requirements for financial transparency and trade execution accountability. Below is an excerpt from the CFTC site:
The final rules include financial requirements designed to ensure the financial integrity of firms engaging in retail forex transactions and robust customer protections. For example, FCMs [futures commission merchants] and RFEDs [retail foreign exchange dealers] are required to maintain net capital of $20 million plus 5 percent of the amount, if any, by which liabilities to retail forex customers exceed $10 million. Leverage in retail forex customer accounts will be subject to a security deposit requirement to be set by the National Futures Association within limits provided by the Commission. All retail forex counterparties and intermediaries are required to distribute forex-specific risk disclosure statements to customers and comply with comprehensive recordkeeping and reporting requirements.
On the contrary, the reason only four firms are currently approved as forex dealer members as of the latest data from the CFTC is precisely because the standards for US regulated forex brokers are so rigorous both in terms of financial transparency and accountability regarding the price where each customer transaction is executed.