It is possible to wear mountain bike or gravel-specific shoes while road cycling with no major performance degradation. These shoes are made with a reduced cleat and some kind of tread which provide versatility to the shoe as well as makes it easy to walk. Road shoes are indeed lighter and stiffer boots, but the difference is not that substantial unless you are competing at a high level. For someone who wishes to do all cycling activities in one pair of shoes, gravel or mountain bike shoes are the best option.