Usually when getting a new rabbit you are wanting to keep them on their old usual pellets(even if they are lower quality, provided they aren't causing serious digestive upset or other health problems)for the first week in a new home, before gradually transitioning them on to the pellets you prefer to feed over the next 2-4 weeks after that. Reason being is that being in a new home can be stressful, which can lead to digestive problems developing, particularly in baby rabbits(and which can prove quite harmful if it occurs), and switching a rabbits food when it's first getting settled in can cause further stress. So it's best to keep everything as familiar as possible for the baby, to help alleviate any rehoming stress it could be feeling.
Hollands can have a sensitive digestive system, so she's right to be careful about what you feed them. But usually that applies to limiting/restricting sugars and high carb foods. It might also include further pellet restrictions(also switching to a higher quality pellet) if the rabbit is continuing to have mushy cecal poop issues. As well as making sure to introduce new foods like veggies/herbs/forage gradually and slowly(keeping an eye out for mushy poop or upset stomach developing), and when switching pellet brands/types. Not all will be sensitive, but many seem to be.
I also agree it's fine not to give alfalfa hay when you are feeding an alfalfa based pellet. It's just not necessary to feed an alfalfa pellet and alfalfa hay to young rabbits, and is what I prefer. Plus it can create problems when they are adults and you try to transition them off of alfalfa and onto a grass hay, as they tend to really like alfalfa and feeding it exclusively as their daily hay can make them very picky about eating other hay. Alfalfa itself won't cause seizures, but if the breeder linked her rabbits seizures to the alfalfa hay, then most likely it was contaminated in some way and that's what led to the seizures.
Just because a breeder isn't feeding a high quality pet food to their rabbits, doesn't mean their advice shouldn't be taken into account or that it's all wrong. Breeders usually do have to feed bulk feedstore rabbit feeds because of the significantly higher costs of feeding a higher quality pet rabbit food. So that's pretty common and nothing wrong with it. Some of what the breeder said may not be correct, but they took the time to give you dietary information and advice on what they thought was the best thing for the rabbit, which means they do care about the rabbits well being.