I think that's adding 1+1 and getting 3.
I've said T&T will persist for years, but it won't be with the aim of preventing a lockdown; it'll be with the aim of detecting dangerous mutations for a booster shot, because the immunogenic response of a vaccine prevents serious illness and, bar a complete change in how the virus works (not the spike protein, I mean in terms of how it actually works inside the human body) and an unprecedented mutation to make it more lethal, that immune response from the vaccine will remain consistent enough to provide a baseline prevention of illness.
No, for me, the reason we actually need T&T and a focus on viral detection in the future is to stop the next pandemic, not necessarily the next COVID strain.
Also, the last bit for me shows the weakness in your argument - we could very well prevent flu killing a few thousand people a year; but the question is whether we want to, given the trade off in civil liberties that would involve. I'd say, clearly, no, we don't. If general hygiene measures like hand sanitisers become more commonplace, good, but we shouldn't be aiming to prevent every death from COVID/flu as the trade off is unviable - notably because by having extreme measures in place you create more death through mental health pressures, people skipping medical appointments for other matters and so on.
People can't just exist; they need to be able to live. It's a balancing act. If 5,000 people die a preventable death in the UK per year from COVID/flu in future years, but it means people live their lives, so be it. It sounds cold to say, but that's just the reality of it.