WP engine never modified WordPress. They took stock Wordpress and edited a configuration file to disable revisions. They didn’t actually change any code.
I thought they'd also modified revisions to have a limit, instead of unlimited. Even when 'enabled', it's not how the rest of the wp installs would behave (iirc). Likely there was some code change there to enable that restriction.
Matt might pontificate about "bastardizing and messing with" WordPress, but this is what he is actually referring to:
A. Single. Configuration. Option.
A. Changed. Default.
Post revisions are a configuration option in the admin panel. They are enabled by default. Some hosting providers (and I expect WPE is not the only one) set it to disabled by default.
That's it.
This is not remotely comparable.
Even without the ACF situation, Matt's description of WPE bastardizing the fundamental offering of WordPress is asinine at best, actively deceptive at worst (and that's where we seem to be, so far).
