I don’t think it’s fair to say they were sneaking it, AoS was always pitched as a more action oriented game than original fantasy - and they ran together for a while before fantasy was retired due to low sales. Stormcast have always been positioned as the poster faction for Sigmar, they’ve been very blatant about that.
plenty of disgruntled ex fantasy players out there, that’s why old world now exists - and the player response for that has taken it from a small side game to a more featured part of their calendar.