First, there are no guarantees other than in respect of death and taxes.
WAT charts define weights (for specific Hp/OAT conditions) at which the certification process determined that the aircraft could achieve the minimum Airworthiness Standard requirements for OEI climb gradient. As such, the WAT chart puts an upper weight limit on RTOW for the day. You are probably more familiar with WAT limits if we refer to them as "(first, second, third, fourth, fifth) segment climb limit"
Has nothing to do with aerodrome length, obstacles, sector length, etc., etc.