Should it 'take this long?', who knows....Can it take this long..deifinitely. It somewhat depends on how often you get to work him or ride him. If it's only a couple of times per week (like me
..), then you need to consider the number of hours per month (or year) compared to someone who gets to work/ride daily. It's a huge difference, so you could cut yourself a lot of slack in that regard.
You don't say if you are trying to ride out solo, or if other people are with you. Many horses get very unconfident being asked to ride out alone and would exhibit the behavior you describe , esp. if they don't see the rider as confident/in control/a leader. that doesnt mean being harsh, of course.
I don't think he and you are anywhere near ready to be cantering ! Until he is solid and obedient at walk, don't trot. until the same at trot, dont canter. That's the safest plan, imho.
Can you work thru this?....most likely, esp. with help from a good trainer. You just need to decide if you want to take whatever time it takes to work thru these issues, or if you'd rather have a more suitable (your words) horse. Absolutely nothing wrong with either decision!! it takes a wise person to be willing to admit they are over horsed.
I was most definitely over horsed. I did decide to take the time it takes, and we have gotten better and better, it's taken several years to get to this point. But, it was better enough to become fun rather than always a fight fairly quickly (sorry, I dont remember exactly, and each horse sets the timeline anyway, so my time is not relevant to what someone else's time might be). Believe me, I feel your pain, and remember well being exactly where you are now.
Is it all you ? yes and no. Yes, he has your number and knows how to push your buttons (been there, done that, got the tee shirt). No, he would test the boundries with whoever is working/riding him, and only someone with more experience/savvy than you (me) would get better results.
Is this as fun as it gets? No,No,NO !! it gets really fun ! Sonny still tests me , but not nearly as often or as persistently. We rode Sunday and he got a bit antsy when my friend and I decided to have our boys stand still while the other 2 riders went ahead on the trail. When I was at your point , he would have blown up and/or blown me up , I probably would have gotten so scared and upset i would have dismounted to feel safe. Sunday , I just persisted in asking him to stay on the spot I picked out , and he quickly calmed back down. (THIS is our spot, walk off and we go back to it...dance sideways and we go back to it,,back away and we go back to it....then he decides that it IS our spot and stands there calmly)
Sonny was a pickle in the arena, too,,before we started making progress. The head tossing,,,oh yeah,,,and I truly believe he was saying 'no! I won't!'. I can't remember the last time he tossed his head with me riding.
It's a hard decision that only you can make. Sonny is now a very good trail horse, and Iv'e decided a good trail horse is worth his weight in gold, so I can offer you hope...but you have to be honest with yourself as to whether you want to put in whatever time it takes. And again, there's no 'shame in your game' to decide that another horse would be more suitable. But,,,and this is part of what made me decide to try to work thru Sonny's issues....the next horse may seem suitable at purchase time, but turn out to be as 'bad' , or worse than him. just something to think about.
keep us updated on how things are going