This is a VERY tough situation to navigate well to everyone's satisfaction. I wish you the best.
It is interesting how much people's experience / position shapes their perspective. From a coach's point of view, I can totally see the basis for a lot of the advice given. Of course, they are going to start with the assumption that the HS coach is halfway reasonable ( understanding the sport, desire work with you to accomplish goals and get along, etc). However, most HS XC coaches are not. It is a government position with little compensation. The less work the better. Anything that causes any effort needs to be eliminated. On top of that, there are additional dynamics that contribute toward most coach's utter crap coaching.
Then, on the athlete's side, obviously a developing teenager is going to be poor at some aspects as well. ALL 14-18 year olds are immature to one degree or another on some things. Typically, they have a hard time communicating well in a productive manner, especially on a topic that means a lot to them. They often come off as very disrespectful and selfish. Further, in regards to keeping things to themselves, they often appear practically incapable of keeping things close to the vest. The lack of nuance and agility that young people often display in these situations is maddening.
If I were in your shoes, I would do the following:
1) I would schedule a meeting with your HS coach where you could spend a good amount of time to express your appreciation for them both as a person and a coach. Include how you know that there is a lot of time and effort required to do what they do (often unseen by anyone). Give them 1 or 2 specific examples of where they did something good or coached well. Finally, let them know of some way that they personally helped you and how you really appreciate it. Spend some time thinking about this in advance to make sure that what you express is genuine. Even if they totally suck, you can find a few good things to praise. Then, I would transition into letting them know that while running is pretty niche, it is very important to you. I would go about it somewhat sheepishly - almost apologizing for it (because you're the "weird" one). Of course, no apologies are necessary, but you are relating and establishing a working relationship. I would include that you really want to run collegiately, but you are concerned because you have a long way to go (even if you are actually somewhat close). So, you feel you really want / need to take your training to the next level. Explain that, again, you appreciate their coaching and the "good" training that the team does, but that you also strongly feel that you need to do a little more (and a little tweaked) than what you've been doing. At this point, you will need to observe how all of this is landing with the coach. If he appears to be a little defensive, then you have probably already gone a touch too far, and it would be best to more-or-less end the meeting there and let him think on what you said a little so that he can get used to the idea of where you are coming from. If he appears to be receptive and happy, then you could maybe continue by saying that this summer you've found some training that really feels like it is good for you. I would not in any way convey that his training is poor and that yours is good... just express that you REALLY like it and strongly believe it is working well for you. As a brief aside, I definitely would NOT say that you got this from anyone else's influence - not another coach, friend, family member, or parent. You got this from your own research and experimentation (which is true, unless the online coach contacted you first). THEN, if he is still tracking, say something very close to, "Do you think that it would be ok if I could slightly modify the training here and there - maybe run a little outside of school practice on my own from time to time?" (This may be a little difficult for you to do well, but I would come across like the coach is in complete control.) You could also add a little extra no-brainer request for permission for improving your diet or something like that. You could add, "I also read that drinking something with electrolytes a couple of times a week is good, and I've been trying that as well. I think it's been good. Is it ok if I continue to do that?" Then, I would finish with saying something nice (and that's true), and be effusively thankful that they are working with you. By the end of this meeting, the coach needs to remember being appreciated, feeling like they are no doubt your coach who you respect, that you have goals, and something something about you wanting to train a little differently and/or by yourself from time to time. BOTH of you MUST be smiling at the end of this meeting in order to consider it successful.
2) Follow up with the coach a week or two later to have your permission to do a little extra. ANYTHING other than him saying, "No, we are going to do what we do and if you can not do that, then you should run elsewhere" should suffice well enough.
3) Consider very thoughtfully the tweaks you believe you can pull off to train well and not raise alarm bells. Can you get out of one of the school's workouts once a week? Can you run some of the workouts at 75-80% and then run a tempo later? There are so many ways to creatively do this, but it needs to be good training, AND you must be able to keep the coach and team happy.
4) Be VERY encouraging to all of your team members. Be the absolute best teammate you can be - even to the ones who aren't initially nice to you.
5) In regards to the numerous races, consider racing them differently (start one at a slower pace and then run the last mile extremely, and then the next week, start out fast and hold on, etc etc). By changing things up, you can make the race schedule work and learn a lot through experience in the process.
6) Implement and execute to your plan. Stay focused. Don't get injured. Give good effort, and trust in your plan. Choose to be a winner.
7) DO NOT ever ever tell anyone else (ESPECIALLY ANYONE RELATED WITH THE TEAM) that you've had this plan and figured out how to effectively run on your own (as much as possible) and still run on the team. If / when you screw that up, and things go south, you can thank yourself for not having the discipline to carry this out.
Good luck, have a great season, and running "career" (collegiately and beyond)!