It's revealing to look at the post-TVC pass rate for ab initios. It's almost unheard of to fail when training is started on SS, KK or Thames APC.
The ab initio pass rate on LL APC must be less than 70% on recent form. Of course those failures usually go on to validate on SS, KK or Thames.
So this would suggest that LL is harder, despite how complex that bit of airspace around BKY is, and how Thames does battle with only two levels, a tiny RMA and RT-blocking eedjits who think it's a LARS.