I'm not sure what the discussion is. Are you trying to define an objective worth? The fact that tens of thousands of lawyers are being paid that much by highly sophisticated employers indicates that it is a fair deal for the employers. I agree that it's likely that if students were graduating with less debt, then the deal would shake out differently, but I don't see that as going to "worth."
I've heard that first years aren't really profitable, but I'm not sure how that goes. At say 400 an hour (lower end), you'd need to bill 487 hours that are actually paid, to hit your salary and bonus, and then let's say another 100 to pay your office secretary etc, so let's say 600 is break even. I billed about 1500 first year--even say half were written off, they still made profit.
have to factor in the availability. as a first year associate, you should make yourself available 24/7. if you planned a nice bbq with family but are the only associate on a small deal that goes crazy, you are expected to cancel and say sorry and go into the office, without a wimper. that is part of the salary, and most other professions dont come with that absolute expectation.
At least at my firm, plenty of first year associate time is written off before going on the bill to the client. except maybe wachtell and similar firms, most partners these dats want/need to have a reasonable bill where the client feels they are getting some sort of a deal. so we tell the client that the first years reviewing 400 leases for change of control provisions will come off the bill and they will only pay for the more substantive work and negotiation. this all depends on client and partner and relationship etc., but i see it regularly.
Still, even though the bills may be written off, its clear the junior has provided value (assuming they didnt screw up...).
as a first year, i think i billed about 1600+ and iirc about 400+ was written off right off the top, plus discounts for certain clients (my firm is great about showing all detail as to billing write-offs and payments by clients). considering my office, my health insurance, my shared secretary etc. and of course the promptly paid bills from clients that were happy to get a deal, my firm didnt lose anything at the bottom line on me. and that's of course also discounting the nature of a minor league system/need to obtain talent by investment.