Benidorm is in Spain. I'm not aware that the Spanish are undermanning their customs posts or applying every rule as rigidly as possible? Or maybe they are, but no-one is going to Spain so it doesn't matter?
There is no doubt that Brexit has given the French the chance to apply some new rules. But there is equally no doubt that the reason for the delays is that French customs could not cope with the expected number of people trying to get into France. This problem will go away in time - either the French will get more customs officers, or they will find a way of processing people quicker, or they will ration the number of visitors, or people will get fed up and go somewhere else instead. But whatever it is, only the French can solve it, and if (as so many people believe) it is entirely down to Brexit, then there is no solution that the French can apply and cross-channel travel will have to be much restricted forever.
What's the general view on the UK's application of the rules? The UK has equally had the chance to slow down admissions by checking and stamping passports, and has chosen not to - presumably because there is no economic, social or security reason to do so. Is the UK in the wrong, or is that a valid option for a country to take?
Having travelled through Alicante* twice in the past three months I can tell you that the same process IS being applied by the Spanish authorities, and it can be carnage. The first time we flew to Alicante this year my wife almost missed our flight, as there were just TWO Spanish staff stamping passports (nb: I have dual nationality, so was able to use my Irish passport, which is an absolute godsend these days). The queues were horrendous. The next time we flew, several people fainted in the queues, which seemed if anything even longer. I guess these events don't make the news because they're taking place abroad, whereas the situation at Dover/Calais (and at St Pancras/Gare du Nord) is different, with each country carrying out passport checks BEFORE the journey, rather than at the end.
[*the airport for Benidorm, obvs]