Yeah, I don't see that problem either. Make all movements being controlled server-sided and then there can't be any "Instant kill monster" hacks. As for exploiting weaknesses - well those exploits can be fixed or simply be considered a legitimate tactic.
I didn't mind that in RO there were tricks to kill off a strong MVP. It still required a lot of training and good teamwork (coordination) to get this working in the first place, so why not reward it? If it's too cheap, fix the exploit.
(Most big RO exploits only worked on private servers anyway.)
Not that RO is a good example though. No exploits is always better. And it's quite possible to not leave any cheap tricks. If you look at any modern AAA title none of them have cheap tricks to kill off a strong boss.
Risk = Reward will always be best.
Regarding stat point system. Well in RO it was so amazing because the structure of the 6 stats: STR, DEX, VIT, AGI, INT and LUK worked so perfectly. Almost every class can make use of any stat. And combined with "cost increases the higher the stat" if often wasn't all so bad to put a few points in any stat.
For example just take INT. On other MMORPG only magicians and healers get INT. In RO any class can make use of INT because it does not only increase magic damage put also the max SP (MP) and SP recovery. And being able to use skills more often is a big benefit for any class. It never hurt to put 10 or 20 points into it.
Or look at the dynamic of damage. For physical classes all stats except for INT matter quite of bit. You need STR to increase your base damage, AGI to increase your speed, DEX to actually be able to hit and LUK for critical hits. But those stats are not stand alone, they influence each other. High damage is a lot more significant if you also attack fast. So STR and AGI actually support each other. The more STR you have the more useful gets AGI and the other way around. But both are useless if you don't have DEX because otherwise you won't hit. But wait, there is also LUK that causes critical which always ignore defense and always hit. So one could also opt for LUK instead of DEX. And the resulting classes are all viable, though they are viable for different situations. A class with high LUK for example is good against monster with high flee or defense, but bad against the rest. A class with high STR and AGI is good against all monsters that don't have a high hit rate because you will almost nullify the damage you take.
And there is so much more.
True, if you just consider PVP, then there are only 1-2 viable builds per class, but in PVE there are hundreds of viable builds, all good for a different situation and location.
Games that just have "Put X stat points per level" almost always end up with "Physical attackers put all in STR, magical attackers put all in INT", because maximizing damage is always the most viable solution. Any single point into a defensive stat will just mean your damage sucks later on.
Regarding the class system, I understood it so that even if you stay Wizard, it's a new class and can't be taken back.
I think of it like RO's class system except that instead of splitting into 2 classes, it splits into 3 classes wheras one class has the same name as the previous class just with added title. They called it "Tier 2" but might as well imagine just putting a "High" in front of Wizard for example.
Q&A 7 is up: http://blog.treeofsavior.com/en/?p=180