It's too late for RMu now but even so doesn't this suggest that the concept of spells need a rethink or at least a reword? Traditionally the casting of the "spell" (I did that because for some it is a prayer and others an act of will) is an action (cue hand waving, shuffling and magic words). What follows, traditionally, was then that 75% of the round was this, yet the effect was seen at the beginning of the round. This begs the question what is the spell user doing for the rest of the round?
Yes, and that was one of the reasons why many people had problems with the original RM2 round. Spells always went first, such that even a 75% spell action was resolved before a, say, 25% movement action. That took a lot of explaining, and quite frankly didn't make a lot of sense at times.
That issue is now resolved in RMU, at least in the RMU phased round, which breaks the round up into essentially chunks of 25% activity. So you would have the chance to move 25% (action phase 1), then another 25% (action phase 2), and possibly another 25% (action phase 3, if you won initiative), before a caster could get off a 75% activity spell.
In the RMU simple round, characters take all their 100% activity one after the other, much like the DnD round, but to compensate, characters have a chance to react appropriately with any defensive actions/spells. In effect, characters finally have a chance to say what they are doing while the enemy Magician spends 75% of the round casting a spell. So if someone tries to get off a 75% melee attack on you, and you are aware of it, you can cast a 0% or 25% Bladeturn in response, and it will take effect before the melee attack is resolved. You can similarly declare parry. This better represents the fact that you would have had a chance to defend yourself if someone started attacking you for three or four seconds.
One final note is that if you removed the 'Instantaneous' designation from Bladeturn and similar spells in RMU (seeing that pretty much all spells are now 'Instantaneous' in the RM2 definition of the term), that would return Bladeturn more to how it worked in RMSS: that is, you would have to win initiative and get the spell off before your attacker for it to have effect.