I swam for 14 years and for 7 at the national level and recently retired. I'm now coaching a (very) energetic group of 8-10 year olds. My rule: you're only allowed to train as fast as you can go before your technique slips, and you're not allowed to go fast at all until you've got the technique down.
When you're racing someone in the last 50m (or the whole race for that matter....), and you decide it's time to leave them behind, you want to be able to go as hard as your body can, and with the proper technique (as that is what will make the most of your effort). When you turn that mental switch on and try take off.....everything but beating the other guy leaves your head, including any technique you were consciously thinking about. At that moment, you fall back on your habits, and if the other guy has better habits...... he will probably win.
It's a long process, but find a very patient and detail oriented technique coach and work with them, even if only on 1 stroke. Don't focus on more than 1 or 2 details at a time; if it were possible to make all of the details happen at once, you'd be doing it already. Instead, take your time in each part of the a stroke (i.e., recovery, catch, entry, etc...) and let the muscle memory develop and let it start to feel more natural in the water. Then start doing progressions to put it all together. All in all, the more patient you are and the less frustrated you get, the faster you'll adopt them. I find with my kids that it takes about 3 weeks before they really start making a habit of something I tell them. When they hit the "on" switch in a race, you can tell exactly which habits went out the window and which ones stuck.
Also, in terms of fitness, I always found dryland training was more effective if I did less of the macro/olympic style lifting and more of the micro movements with scapular stability, core strength and endurance and balance.
Looking at other things, there are plenty of places in training or a race you can be more effective. I always tell my kids in a descending set to descend by being stronger, and smarter. Stronger is obvious, but smarter can mean maybe going further off each wall, breathing every 5 instead of 3, taking more strokes out of a streamline before breathing, etc....
Hope this helps!