Saying that it "never runs into our DR" is equivalent to saying that Reinforce Shield or Halting Vortex mean we never actually get hit, which from experience is... demonstrably not true, because we're fallible and sometimes get hit in ways we did not expect. There's obviously a value to having DR as well as ablative health or perfect defences.
It's the automatic turn end for Reinforce Shield breaking that does it. We can easily wind up getting hit but only in very niche circumstances does it happen after Reinforce Shield is broken but before a turn end and thus the opportunity to use Slowing Slog before more attacks anyway.
So there are, realistically, three likely possibilities:
1. We don't get hit. Slowing Slog is wasted.
2. We get hit but Reinforce Shield stops it entirely and still has juice. Slowing Slog is again wasted.
3. We get hit, Reinforce Shield stops it and breaks...this ends the turn, meaning it's a new turn and we can activate Slowing Slog then.
The fourth possibility of Reinforce Shield getting broken and it not being a turn end is probably possible, though it's literally never happened yet, but it seems unlikely enough I don't think we should bet on it happening.
Now, once Reinforce Shield is broken, it takes actions to set up again, while Slowing Slog does not and Slowing Slog becomes much more arguable, even optimal, but not with Reinforce Shield still going at the beginning of combat.
It feels to me that you've gotten stuck on arguing this point and are putting an unreasonably high value on nine orthstirr in order to arrive at the conclusion that it's not worth it. Compared to what we have spent nine orthstirr on in the past and doubtless will do in future, it is worth it for the Stoked Die alone given the zero opportunity cost of using it, before we get to the DR. It effectively means with that and Fanned Flames that we have the equivalent of a Fight of Your Life ready to go always, at all times.
We were very specifically warned that efficiency matters more now than it ever has before. I don't think taking that to heart is unreasonable.
Also, once again, Fanned Flames doesn't add to Stoker State dice. And Stoked Pool is all or nothing on Contested Movement or most other uses...only on Stoker State Tricks is it what you imply...and there's a reason we save FoYL for Contested Movement, it's so much better there. And +3 dice when used on non-contested movement can be duplicated with 3 Orthstirr at most...spending 9 on it is kinda dubious. It can also boost damage and other effects on some Tricks, but 6 extra Orthstirr for +1 damage on a single attack is a pretty mediocre return on investment.
