Is there any point to SQL partitioning if I index properly and avoid full-table scans?
Partitioning has a few other benefits as SQL Server almost sees it as a brand new table.  Thus it will use more threads and run concurrent scans on the GAM/SGAM/etc. pages to find your data.  It'll also lock only that partition if it needs to escalate which is a nice to have, assuming you are partition aligned.  So if you're running a query that hits multiple partitions and you have partition elimination working, it will be able to do the metadata lookups and scans on all those in parallel.

It gives you the benefit of having a particular index for the top (or first) partition when it is queried so heavily but drop the index or add other ones for historic data.  This way you can maximize your index usage that way as well.  

You can even compress data per partition if you'd like, although you're using newer versions of SQL Server you might get some good compression per partition or just table.

There could be more but those are the main ones I can think of.