I disagree. There was a case some years back where the son of a farmer worked most of his life (decades) on his father's farm for a pittance because his father told him that the farm would be his on his death. There were no other children so the son accepted this. When his father's will was read he had left everything he had to an unknown child of an extra marital liaison.
The son went to court and, if I remember correctly, won his case, on the grounds that he had led a restricted life with his parents and it was his work that had made the farm the valuable asset it was on his father's death.
There will always be cases, where someone has a right to expect proper provision in a will and can dispute any lack of provision.
Bear in mind that, if all the beneficiaries agree, a will can be changed after the death of the person who made the will, quite legally, by a Deed of Variation. DF left all his estate to be shared between my sister and myself. We made a Deed of Variation to include his DGC among the legatees.