Like a lot of things, it depends how native-like learners want to
sound. (The equivalents of) those sounds are dental in many (most?)
European languages, and speakers of those languages can easily speak
English with a dental setting. (Dunno about Japanese.)

A word like 'strength' - or even better, 'strengths' - is difficult
regardless of that, because of the clusters. It's difficult for native
speakers, too, who tend to reduce it to 'strenths' or 'strenss'.

But for someone who does want to sound like the natives, getting the
right articulatory setting is likely to be a more efficient and
effective approach than trying to get all the phonemes exactly right.

Bryan Jenner wrote about this ('The wood instead of the trees') in
issue 2 of Speak Out! (before it was actually called Speak Out!) in
1987. The term 'articulatory settings' goes back at least as far as
Beatrice Honikman (1964). The concave tongue shape is one of the key
features of the setting for English. (The others are: loose, inactive
lips, neutral larnyx position and generally relatively relaxed speech
organs.) It determines the exact qualities of the consonants that Alex
listed, and also, of course, has an effect on the qualities of vowels.

(It's suggested that a convex tongue setting among certain groups of
early Indo-European speakers predisposed them to the palatalisation
that eventually led to the split between 'centum' and 'satem' languages.)