The prohibitive spell point cost is not the direct issue but it is along the lines of the issue. If I am a typical caster, I have XX mana to spend on a given set of encounters. The goal of a successful caster is to find the most effective and efficient way to use this mana. So let's look at the possible ways to spend mana.
1) Buffing - Playing a buff-bot is not exactly fun for the vast majority of the player base. This is why buffing is such a demand at lower levels / lower mana pools; but come higher level this is relatively balanced so that buffs can be cast without significantly weakening the player's mana pool. Additionally, if buffing is the priority position of casters, no one will want casters, because a bard can do it better.
2) Nuking - This is a very popular use of mana throughout the mid levels where firewall is king (and the old cloud kill was often used in a similar way). The problem with this, though, is it obsoletes melee classes. I think Turbine did a good job of recognizing this issue, but unfortunately have only responded with various workarounds so far (fire resistance/immunity, removing the ability of firewall to stack, etc). Balancing the nuking ability of casters with the sustained DPS capabilities of melees often results in casters that are out of mana extremely early in a quest (dull/boring for them) or casters that are so powerful that melees are not wanted (unbalanced).
Historically, the reduction of the value of nuking made crowd control a valid choice in how to spend mana.
3) Crowd Control - IMO, the development team should strive to make crowd control the most effective choice in how a caster spends their mana. It is fun for the caster, who feels like they are contributing to the fate of the party as more than just a buff bot. It is fun for the melees, because they are still able to contribute reliably outside of sustained DPS raid scenarios. It is also better for the cleric who possibly can contribute in other ways to the party rather than being glued to red bars.
The more that crowd control options are limited, the more casters are either going to switch to nuking, or not even be wanted in the party as compared to the better buffs of a bard. Nuking is much harder to balance and to retain the ability of the melee classes to stay relevant.
So in conclusion, you are skimming the tip of the issue in regards to the prohibitive mana cost to re-cast. To be more specific, though, the more "re-casting" becomes necessary, the more these crowd control spells are just not going to be used in the first place. This reduces the caster classes to either nukers and/or buffbots; the first of which is extremely difficult to balance, and the second of which is both boring and inferior to a bard.
Keeping crowd control as the preferred option for caster use of mana is probably the most balancing way to do things, and considering how difficult it is to already land most crowd control in endgame, any further reductions in its viability would most likely result in it not being used at all.
Hope this helps![]()