I have to concur with the OP.

This is an international game. Unless something magically changes, someone will always be having some form or other of lag issues, be it related to the servers being in distant Japan or their own service being somewhat less reliable.

Being able to queue the next spell ensured that players (myself included) were not disadvantaged as a consequence of the lag. But now, it seems I'm relying on a guess as to whether or not I'm ready to cast a spell or not.

The worst bit is, you can still make the input and without any form of error message. So you may think it was ok to start your next spell, but you don't find out it wasn't until you're realizing that nothing is happening. Things start clogging up, and you get frustrated because that was valuable combat time you could have been making use of to not die in the now harder content.

Something needs to be done. If the queuing is not to be reinstated, then the ability to input in such scenarios needs to at least be visually restricted to make it 100% clear what position your caster is in, regardless of latency. Ironically, the easiest solution to this in my opinion would be to allow a spell queue.