I'd second this. You're in a lousy position. Views to imitate schema may be one of your ways out of this. Throw in indexed views and you might be looking at a possible short term solution while you puzzle out what the table level should actually look like.

Can you take us step by step through your 'large data load', including existing rowcounts, expected inclusion volume, number of tables, if you use staging tables to cleanse the data if there's any cleanup to be done, etc?

A reindexing every load isn't unheard of, but it does depend on the volume. It also depends on the 'noise' area in the table. Most huge tables have a very small area that's being heavily updated with the rest of it just being there for reference, if at all. I've seen as low as 2% fragmentation on a huge table be enough to take the processing speed of a system down.

At the time, I didn't have easy partitioning available. However, if you can isolate this to being a portion of your issue (which is what it sounds like to me offhand), it may be a possibility. The biggest reason to do this is reindexing will be much faster in the area(s) of the partition that don't involve the remaining large volume.