Ok, the basic rundown as I understand it is that when a tobacco is available in both tins and bulk the difference is because the stuff in the tins has started anaerobic fermentation already. Also consider that bulk may be packaged and shipped much sooner than the tins which may sit at the factory for a period before going out to the distributor where they may sit again for who know how long before being shipped overseas to the importer where the tin may once again sit before going to the individual stores. There is also the possibility of something like driving going on with the tins of they are shipped in hot weather. Those shipping containers can easily reach 160-180* inside during a real hot spell. Sealed tins at that temp for extended periods could have their fermentation sped up or even have the sugars start to caramelize.
The difference in price is something you have to decide if it's worth it to you. Also as pointed out by Pete some blends are not and will not ever be sold in bulk. Like Dunhill Royal Yacht. I wish it came as a bulk but I'm guessing the fermentation in the tin is a part of that particular flavor profile that just can't be replicated in a bulk. Also as to price its pretty expensive to package out small units, it takes a lot of time and uses lots of materials as opposed to one big 5 lb plastic bag.
Hopefully I was able to make this clear as mud for you.
The only thing I can add to the brief but pertinent discussion — at some point, pipers may move away from pursuit of an absolute, perfect blend, and begin to go steadier with a limited number. When we reach this point, we move toward bulk, if possible. And with the price of tins increasing, now is a good time to speed up this sequence. Now that the cost of the tin exceeds the value of the diminishing quantity of tobak inside it. I expect to see the standard packaging to be a pouch. Entropy: Things change for the worse.
Thankfully most of my favorites only come in tins. I hate having to jar stuff as it takes up too much space. There are a few blends in my cellar that come in bulk and tins. Samuel Gawith Best Brown, St Jame and Full Virginia Flakes are three and I do have more bulk than tins as that was all that was available when I started cellaring it in 2012.
One example of a bulk being not as good as the tin is Hamborger Veermaster. When it was re released I bought a pound and there was a bunch shake in the bottom of the bag. Only bought tins of it after that.