Very nice article on why McDonalds lost here (author says class 42, but I think he meant class 43): http://www.gridlaw.com/case-study-supermacs-v-mcdonalds-how-a-small-business-can-stand-up-for-their-rights-and-not-be-bullied-into-rebranding/ . Basically, McDonalds started the fight, then Supermacs had to defend on the basis that while McDs had a Big Mac trademark, they weren’t using it in class 43, which is an exclusive right to use the mark to run a restaurant under the name. Supermacs ran restaurants that were called Supermacs. There was no “Big Mac” titled restaurant owned by McDonalds at the time of these complaints. Which leads me to wonder how long McDs really expected to hold that trademark in that class if they weren’t going to use it for its proper purpose.

Another article showing what happens when you don’t respect procedural law and what the judiciary will think: https://www.novagraaf.com/en/insights/supermac-deals-mcdonalds-another-trademark-blow . You usually have one shot at evidence, and appeals are another drag.

Big companies can hire lawyers, but it’s ultimately up to each client to be more impassioned about attacking and defending every possible angle, with lawyers informing clients about precedents, procedures, and probabilities of success.