No. First, you usually need both, Want= and After=. Second, that After= isn't really "after" in the traditional sense, because systemd will start A, not wait for A to be up and running and immediately after the "A has been started"-event start B. If you really want A to be available when B is started (which is the traditional init-script sense of "after") you need to modify the software A to signal completion to systemd or you need some horrible shellscript cludges in the Exec=-line of B that checks for the availability of A. Or an inbetween unit with a Exec=sleep 5 or something.
Claiming "it is just 1 line" is either inexperience or dishonesty.
Not really, it's just one simple line in a unit file. (https://fedoramagazine.org/systemd-unit-dependencies-and-ord...)