Haven't read all replies, so sure to repeat...
The diet you feed is seen as 'high octane' because it's high energy. Oats are high in starch(so energy) and also alfalfa/lucerne is high energy, although low in sugars.
As far as grain goes, I think oats are not terrible, and they are one of the few grains that are reasonably digestible to horses when fed whole(I'd still prefer processed, but other grains *need* to be processed for horses). But grain is high in starch & energy, generally not needed for the average horse, unless in hard physical work. Starch can also wreak havoc in a horse's hind gut and cause a number of issues, laminitis being one. So I would generally want to avoid feeding high-starch, grainy rations, in favour of a healthier alternative if high energy/extra calories were required.
Alfalfa/lucerne is a great feed I reckon. Being low in sugar, it can be a good feed for laminitics too. But it is also quite high in energy, so should be fed judiciously - or not at all - to 'good doers' or horses who are getting well enough calories/energy elsewhere. It is quite high in calcium, protein & other nutrients, which can also make it a valuable part of the diet, but being very high in some nutrients & not others(as someone pointed out the Ca/Phos balance for eg), should be well balanced with the rest of the diet. High protein can also be problematic, esp to older horses.
So.... IMO if for whatever reason I couldn't find a better alternative for the horse in question, I would perhaps consider feeding your diet to a horse in hard work or needing 'condition', giving only a very small amount of processed, rather than whole oats, over at least 4 small feeds daily, and would be giving the lucerne as *part* of the horse's forage ration, making the majority straight, unimproved grass hay. I would also do a diet analysis and supplement the horse with whatever nutrients it was lacking/imbalanced in through this diet.