Expontential Experience Spending

Having GMed at least one gathering, crafting and combat skill I've noticed a trend in all three and think that it needs to be part of the conversation. I also think it contributes to a lot of feedback we see about experience pools and how to deal with them. I'm going to be using an example from Gathering in this thread but i think the issue exists to some degree across the board. Specifically, I am talking about the maximum XP "spent"(taken from pool to skill) and how it changes.

Math/Experiment Section: (You can skip to conclusions if you don't want to get into Details)
XP Pooled per level 5 mining node: 500
Success Chance on level 5 mining node: 66%
Mining Proficiency: 73
Swift Gathering - Mining: 100
Pooled Producer Exp: 915k

From previous experience while training swift mining, i knew that the XP gained from resource nodes while gathering changed a lot in the 80's of the skill. I always gather with exactly 1 skill turned on, and also know from the past that all 4 of the gathering skills in a tree take the same amount of XP to train. I also can state confidentially that the XP is pooled only on success but is spent on every skill use. level 85ish (with ~62% success chance) was an extremely important time for me because it was when i transitioned from gaining XP when gathering to losing it(over time). Level 90ish was also important because that was when i transitioned from losing experience on average to losing experience even on success.

The amount of xp gained when gathering is equal to the node XP pooled minus the XP spent on the single skill used. In this case I have a mining skill above and below the 80s, so I think it can be used to effectively illustrate the situation.

Level 73:
XP gained on success = +335
Node XP = +500
XP Spent = 165

Level 100:
XP gained on success = -415
Node XP = +500
XP spent = 915

(Note: At 915k i am not sure that i am spending the maximum for GM - i know for a fact that it dropped to spending 913 when down to 905k pooled XP)

Conclusions:

Increasing skill level by 27 resulted in increasing the amount of XP i spent per use by AT LEAST 554%. This is probably because the max XP spent is proportional to the XP needed to gain the next level(which is likely exponential), and i think that this design is a mistake.

I understand that exponential XP per level is quite common, and that by decreasing the XP pool, you will end up spending under the maximum XP per use. Some might consider that mechanic to be self-correcting - it is not. The reason this is not self-correcting is the fact that it drains your pool BEFORE it corrects the rate at which you are spending XP.

While losing the pool might not seem like a big issue from a design perspective (At the end of the day XP spent on skill <= XP gained from nodes), it offers a significant psychological impact. At lower levels of skills, people get used to watching an experience pool go up. As the skill increases, that level of pooling slows, and to counteract it, they must find ways to improve their XP pooling intake. If the transition is too rapid, there is nothing they can improve to keep up with the changes.

This means that unlike before they must watch something they built up decrease. Additionally, this means that training any single high level skill slows how fast you can train low level skills. At 915k experience, I might not have maxed the gain rate for swift gathering, but i did max the gain rate for mining proficiency. If i spend 500k (easy enough enough to do at 900ea) training swift gathering, I no longer have that max gain rate. That means that any time someone trains a high level skill, they don't need to just deal with gaining at a reduced rate but also they need to rebuild their XP pool after the fact, to even get their gains on other skills.

I propose that the max XP spending rate reduces its degree of acceleration. It can still correlate with the XP needed to increase levels but it should not change so quickly that the player experience drastically changes within a few levels. With the reduced acceleration, it might also be better to make the max experience spending larger at smaller levels, as to prepare players for the higher level experience and to not throttle high level xp gain too much.

Note: Skill gains that require consumables(particularly things like poison/crafting more than spells) should probably have an across the board higher xp spent per use compared to other skills.