EXP to next level specifies how much more EXP is required to reach the next level. To calculate the Total EXP earned so far for a level, add the Total EXP earned so far value of the previous level and the EXP to level value of the previous level. For example, to calculate level 3's Total EXP earned so far (49), add both level 2's Total EXP earned so far (15) and EXP to next level (34) values.
The EXP tables have undergone several revisions over the years, as Nexon has attempted to speed up the leveling process overall and for different groups of levels.
There was the initial table with the maximum level at 200 and the total EXP needed was 38,703,363,662 while the strongest monster Skelosaurus gave 4,500 EXP each at 1x EXP rate.
In the Time Temple and Pink Bean Boss release patch, EXP needed for Level 10~30 was cut by 33% and Level 31~199 was cut by 20%. Total EXP needed to reach level 200 from level 1 is 30,950,360,817.
In the Big Bang patch, there was a revision that reduces the overall EXP to get from Level 1 to 200 by 37.58%. Specifically, the total EXP was adjusted differently as such (it does not mean each individual level gets reduced by the same %):
Getting from Level 10 to 30: Reduced by 68.76%
Getting from Level 30 to 70: Reduced by 75.42%
Getting from Level 70 to 120: Reduced by 63.11%
Getting from Level 120 to 200: Reduced by 37.21%
In the Legends patch, the new concept called Link Skills were added, which basically forces everyone to train the new jobs that was released to gain additional benefit to their main character. All new jobs released has a link skill.
In the Justice patch, another new system called Character Cards was added, so players will need to train a total of 6 characters to Level 200 (max level) for maximum effect.
Tempest patch altered the levels that applied to third and fourth jobs, so the EXP was adjusted minorly so that Level 60~64 and Level 100~104 will have a constant EXP requirement instead. Other levels were also adjusted slightly due to rounding.
In the Unlimited patch, Character Cards was modified to allow 3 more characters up to Level 200 but disallowed duplicate jobs. (Total 9 characters Level 200 for full effect)
The Level cap was then raised during the Cygnus Returns patch, for the first time in 10 years, from 200 to 250. Existing EXP for below Level 200 remained the same.
With the introduction of the 5th Job Advancement during the V Patch, since it requires Level 200 to start the Job Advancement, the EXP curve is once again reduced for up till Level 200. The total EXP was adjusted by 29.58%.
In the Beyond patch, Character Cards were replaced by Legion, which basically requested 40 Level 250 characters for absolute maximum effect. As it is just downright impossible, majority of the endgame players settled for 40 Level 200 characters, which is classified in the same tier of ranks as 40 Level 250 characters (Grand Master Union).
In the Black Patch, as people gather up to take down the Black Mage, the total EXP needed to get from Level 200 to 220 was reduced by 24.7544%. Specifically, the total EXP needed was adjusted differently as such (it does not mean each individual level gets reduced by the same %):
Getting from Level 200 to 205: Reduced by 14.6306%
Getting from Level 205 to 210: Reduced by 39.5375%
Getting from Level 210 to 215: Reduced by 27.4463%
Getting from Level 215 to 220: Reduced by 20.3384%
For the purposes of Level 3 Link Skills: Total EXP needed to get from Level 200 to 210 was reduced by 32.3974%
For the purposes of Legion: Total EXP needed to get from Level 200 to 212 was reduced by 31.1011%, from Level 200 to 213, total EXP reduced by 30.3991%
For specific changes, you can view it here. (Credits to Grey of Southperry)
In the patch after the Black Patch, the maximum level was raised from 250 to 275. Existing EXP for previous levels remain unchanged.
In the Glory Patch, the total EXP requirement to go from Level 220 to Level 235 is lowered by 25.1736% (each level is adjusted differently). Specifically,
Getting from Level 220 to 225: lowered by 31.2216%
Getting from Level 225 to 230: lowered by 10.8712%
Getting from Level 230 to 235: lowered by 29.2432%
In the RISE Patch, the total EXP requirement to go from Level 170 to 200 is further lowered by 18.5652% (each level is adjusted differently). Specifically,
Getting from Level 170 to 180: lowered by 6.7982%
Getting from Level 180 to 190: lowered by 16.0243%
Getting from Level 190 to 200: lowered by 23.6185%
Final evaluation points
While levelling has been made much easier, players are now also expected to make multiple characters (up to as many as 40) so that they can benefit from Link Skills and Legion, as shown by the bolded points above to how demands have grown (6 --> 9 --> 40). Instead of training 1 character, now players will have to train 40 characters, even though training speed has been improved drastically (compared to the beginning).
While link skills only require up to Level 120 for the full effect (Level 210 for an enhanced effect for some skills) for up to around 20 characters at max depending on individual needs, Legion expects 40 Level 200 characters (level sum of 8,000) to be able to almost fully utilise the system (Legion Rank will be at Grand Master Union 1), whereas Level 200 used to be the maximum level. Even for a subpar effect, it still expects 40 Level 150 characters (level sum of 6,000) to unlock the entire board space, or Level 140 to get the same tier of effect as a Level 100 Character Card (replaced by Legion system).
This shifts the focus away from the conventional "focus on 1 character" like the beginning, to making multiple characters to benefit that 1 character or the whole account, leaving less time for that 1 character.
However, it may also be good for newer or more casual players as they can easily change job if they do not like their playstyle as much, so resource wastage will be minimal (but they should still get it up to Level 140 or even Level 200 if the job has a powerful Legion Attacker effect)