Sorry I failed to respond earlier. I can understand your impatience, building a big aerobic base is slow. But bear in mind that you aren't just training for this season. It takes competitive cyclists years to reach their genetic potential, even at the training volumes put in by the pros. Merckx, who was a prodigy, didn't race the TdF until a couple of years after he'd started winning the Classics because he knew he hadn't reached his full strength and he wanted to win, not just take part.
When you say that at 126 bpm reciting the alphabet is a little difficult, you highlight one of the shortcomings of judging progress by HR. it sounds as if VT1, for you, is happening just below that HR. That may change, your aerobic threshold may climb a few bpm. But more important is how much power you're putting out at that level of exertion. That's what you ought to see change over time. And there's absolutely no disadvantage in having a huge aerobic base. Yes, of course you have to train the top end as well, but improvements there come along relatively quickly. There are big disadvantages in training for speed without having the base in place, though, (unless you're a track sprinter) it's self-limiting.