I think the TK70 is still very relevant and so are many older flashlight models that may be one, two or even three years older.
In fairness, assuming overall quality between a latest model and an older models is on par, whether a light is still relevant should be decided based on UI, runtime, and brightness needs.
Even if an older model and a newer ones are identical in all respects except brightness and to a smaller extent runtimes, if the older models provides enough lumens and candelas for your needs, it might still make sense to go for it over the newer model, especially if in doing so you can get an excellent light at a lower price. As somebody put it a few posts earlier: "the dark didn't get darker" or to put it differently outside it isn't darker than it was 3 years ago!
If an older model and a newer one are identical except for the LED which gives you more lumens and longer runtime and by getting the older model you don't save any money or don't have a budget constraint, then maybe getting the older model does not really make sense: if I could get more without a trade-off, I'd go for it.
On the other hand, if the older model offers a UI and/or form factor and/or battery compatibility and/or beam profile and/or better bang of the buck than the newer model, going for the latter just for that 10%, 20%, or even 30% extra brightness when the older model is bright enough for our needs, clearly shows a tendency "lumasochism" - i.e. inflicting ourselves pain just for the pleasure of having more lumens! Unfortunately, I have to say it took me a few buys before giving up the obsession of doing comparisons between flashlights down to the last lumen and those 5 meters of throw that should only be considered after everything else has been weighed!
Aside from the extra lumens, often added at the expense of good runtimes just to sell more, everything else still matters: even discontinued older flashlight models!