You are right in that LACP bonding methods cannot increase the throughput of a single flow to gt any single link in the group (the balancing method can utilise src/dst MAC, IP and sometime L4 ports).

MPTCP establishes multiple subflows across individual IP paths and can load balance or failover across all subflows. Applications do not need to be rewritten to take advantage of it. I'm not sure if that includes kernel modules like DRBD though. I suppose someone needs to find out :)