When you MB with Ancient Magic, the BLM does indeed start the skillchain, because the cast time on those is SO LONG that he actually has to start casting a good 4-5 seconds before the skillchain starts, lol. I haven't played BLM to those levels personally, but my husband has, so I have more of an insiders view than most.
TP calls are essential for him. They help me as RDM too, because I'll change up my Haste order depending on whose TP is higher, in order to get both melees to full TP faster. Whem he gets a full TP call, he then decides, based on how much life the mob has left, whether to do an AM burst or a standard 3 spell burst. If the mob has enough life to make the AM burst worthwhile, he'll start his AM macro, which is something like:
/ma "Freeze" <t>
/p Casting Freeze
/wait 5
/p Ready to start skillchain!
If it doesn't have enough life (generally less than half life left, heh), he'll just say "Go skillchain" and throw a Water 3 at the end.
Either way, he absolutely needs those TP calls to be prepared to cast for the burst. At the lower levels, you can oftentimes throw a level 1 spell at the last second and still connect, but once you get into the level 3 spells, you have to actually start casting just before the 2nd weapon skill in the chain is firing to land the burst. If you were doing something else because you didn't know people had full TP, then you're pretty much screwed.