[@Moonlit Sonata]
Shouldn't you have waited for the other characters to have posted before issuing your response? Rostam was being supported by 3 Archers during his charge, all of whom are going to get shots off before his Charge is complete. The idea of advancing under ranged support is that the target has to fend off ranged attacks while the melee unit approaches, hence protecting him from being singled out. Maybe all three archers do decide to betray him and not shoot, but we really don't know that yet. You broke posting order to launch a killing blow, while ignoring everything everyone else might be doing in the remaining time. 

On speed related matters, I'm not thinking in terms of breaking or not breaking the sound barrier or anything like that, nor did I think I was expected to. Most, in fact, all Role Plays I have been a part of don't do this, simply because of how complicated it makes everything, especially with humans running around at 10 and 20 miles per hours at the same time. 

If you are going to apply these standards, you should have told me first, and assigned an exact speed for Rostam and his Mount during the character creation.

The points you make about Servants being able to turn faster than their mounts can is moot since I assumed that either way it would be fast enough. I even factored this rule in by having Rakhsh take a sprain from turning faster than horse's are meant to on this occasion.

For trying to tank out the attack, you just finished shooting Rostam with an arrow, and telling me I was foolish to try and tank it. Noble Phantasms use difrent standards of power to ordinary attacks, and there is no case I can think of of a Servant surviving a direct hit from an A rank one, except for Hercules. 
Besides, if Rostam can tank this attack, then shouldn't he still be alive anyway? Trying to dodge it doesn't lower his passive defenses, and since it's a wide range blast, holding his mace out or something isn't going to do anything. 

Dismounting from the horse and then jumping away would have taken longer in this case, since it takes a moment to free yourself of the saddle and then change directon. I knight cant just spring out of the saddle whenever he wants.  
When Alexander escapes Excalibur, he is jumping from a moving platform which he is already standing upright on.

Not attacking at all I guess is an option, but I already exercised that option when I had him take his Master away to safety first. 
When Rostam charged he was not charging head on, was ready to prepare evasive maneuvers, and he was being supported by 3 archer Servants, who you didn't let post. This hardly counts as reckless, in fact, I cant honestly think of any better opportunity for a mounted melee character to try an come to grips with a ranged one. 

I really don't see any circumstance which Rostam could have survived this, aside from not attacking at all, which I had already done. Continuing to delay longer would have been bad characterization, as well as being tactically bad. 

I have sunken over 15 hours of my limited free time into this character and this RP, and you have eliminated him before he was able to have a single extended encounter with anyone besides his summoner. 

I would like to request a revision of these last few events.