For Reference
In LSMW, below 5000 records are updated where as incase of BDC we can upload more than 5000 records at a time
LSMW use to upload the data from flat file. BDC also used to upload data through flat file it works through an ABAP Program.
SAP official statement is that all of BDC is no longer supported that doesnt mean that we cant use it, It just means that if anything goes wrong with your BDC Implementation . They wont help you with it Many still use BDC with great care.