220v, 3-wire circuit, 4-wire cooktop: tying neutral & ground – variation on common question

220v, existing 3-wire circuit, new 4-wire cooktop (I understand that white and ground on cooktop get connected to bare ground on incoming line).

BUT, the 3-wire incoming line first goes into a junction box which feeds a 220v, 3-wire undersink tankless water heater. That same 3-wire line then goes to the new cooktop where the white neutral and ground are tied together. The cooktop has an integrated fan so I’m sure that the neutral and ground will be part of an active (i.e. “live”) 120v circuit.

QUESTION: is this dangerous? Logically if it was dangerous, any instructions suggesting tying the neutral and ground together would also state that the neutral and ground can ONLY be tied together on a dedicated circuit, which the instructions did not state.

So logically, this setup should be safe. Having said that, “logic” has gotten a lot of people killed!

Any comments would be greatly appreciated!