Whoever the operator / whatever the brand overcrowding on the route and across to the coast has been a problem for years.
Aside from London Underground when central London lines have been closed the most overcrowded train I have even been on was what should have been a Birmingham-Holyhead ( or if not Bangor ) service in 2014. Starting from Birmingham International as a 2x 2-car 158 set combined Holyhead and Aberystwyth service most seats were taken from New Street then to Shrewsbury overall more joined than left so plenty standing. At Shrewsbury the set for Aberystwyth split. Now every possible space used for standing including the toilet. Plenty were left on the platform. Departure inevitably was late then every station a long stop for those who wanted to get off to make their way to a door and any wanting to join try and squeeze on. I left at Wrexham. Looking later at RTT the service was terminated at Chester. There was an extra Chester-Wrexham-Chester so logically the set was used for this. How passengers for stations Chester - Holyhead ( or Bangor ) completed their journey I have no idea. Likewise how the booked return from Holyhead ( or Bangor ) was covered / how passengers reached Chester.
Years before I was at Shrewsbury on a West Midlands Day Ranger. The platform for the next Aberystwyth service was heaving. I don't know what actually ran but a rake of stock was needed not even a 4-car DMU. Seeing this has totally put me off a day trip to Aberystwyth ever since.
As discussed elsewhere e.g.
here the number of coaches retained and only used a few times a year by the Beeching era was unsustainable. However not being able to significantly increase capacity at certain times equally is a failure. Between peak summer, sports and other events there ought to be enough ticket sales to more than cover costs, again discussed on other threads.