Actually there are alternatives for 216M, like 215X/GMB24
If you consider the bus-bus interchange,
it's not appropriate to say 215X is the alternative for 216M,
of which passengers intended to change for some territory routes like 42C, 258D, etc.
The coverage of 215X can only serve most who just moved from cross-harbour route or MTR instead of those in opposite direction or via Yau Tong.