It really depends on what your quality of instruction was before.
An instructor/trainer who wasn’t a good fit, is uneducated, questionable morals/judgment or a “shingle-type”, etc? Yeah, you’re better off going out on your own.
But a good instructor or trainer with expertise in your discipline? No, I don’t think there is any benefit to avoiding what they have to teach you.
@Renn_aissance hit the nail on the head with tips on how to be trainerless; it really requires you have a solid foundation and understanding of setting training goals and reaching them – as well as having a solid effectiveness of the aids. You need to have an open toolbox, especially if you are bringing along a green horse versus riding a horse confirmed at the level.
I’ll add something: Know your riding weaknesses, but don’t get into your head. To really improve, you need to be a self-starter that is diligent and self-aware. These aren’t buzzwords: without an eye on the ground to ‘fix’ tiny details, you can sometimes lose your position and your effectiveness overtime. You have to cognizant of your rides, analyzing what was good and what was bad - and sometimes without an eye on the ground it can be hard to see the whole picture. Every now and then I’ll ask my SO to film a ride of mine, so I can go back and see what I need work on in my position and my aids. And then you need to consistently apply it – every ride, every time you feel your hands get too low or your shoulders round. This is hard to do.
The largest challenge I’ve had as someone who has been “outside” of a program for the last 15 years is that I don’t tend to push my horse[s] as hard at home as I do under the expert eye of an instructor. This means that while my horses are very thoroughly brought along, it hasn’t been as quick as it would be in a program. If you’re okay with taking time, this is alright – but you have to be careful, because before you know it your green 5 y/o is still green at 7 and then at 13 is only doing middling levels in your chosen discipline… Horse years are golden, and don’t last forever. We only have so much time with each horse and it is truly amazing how quickly time passes by.
Another thing to consider is, if you keep your horses at home or outside of a program, you might not have access to the same training amenities as you would if you went to a trainer. I don’t just mean the perfect-footing ring where you can really focus on the quality of your transitions – things like poles and cavalettis and jumps are expensive and break down over time. Do you have access to these sorts of things, where you can jump a full course at home? Or do you need to truck out? There’s value in being with a program purely for the physical things it offers: a ring where you don’t need to fight the footing, easy access to jumps and courses, and access to venue-specific things like an XC course or trails.
My instructors know I operate on my own time. They are wonderfully accepting of the fact I am outside their orbit: I come to them once a month or so, and they give me homework – and I work hard on it. If I don’t hear in my next lesson that “wow, big improvement on XYZ”, I know I’ve really slacked off and let myself down. So you need to be hard on yourself too – but not in a way that damages your confidence or sets you back. You need to be visually seeing improvement – set a time-sensitive goal, and work towards it. Otherwise, you might find you just wade along when you’re totally ready to jump into the deep end.
I love not being in a program. I get to have my own agenda, bring my horse to my instructors when/if I have the time and budget for it… but it comes with trade-offs. You just have to figure out if they are worth it to you.