More specifically, it chooses by cumulative work. Bitcoin needs that behavior because of retargetting (a lesser height chain may have required more proof of wor

More specifically, it chooses by cumulative work. Bitcoin needs that behavior because of retargetting (a lesser height chain may have required more proof of work to build than a higher height one). If your custom blockchain has a static target, choosing the best chain by height is perfectly fine. Though, I'm not sure how useful a blockchain without retargetting or POW would be.