You are correct: some present participles have developed into adjectives so much that they can be used as the nominal part of a predicate, typically after "het is ..", not so much for persons like hij, jij, ik etc.
Het is vervelend
Dat is opwekkend
De zaak is nog lopend
Deze uitspraak is bindend
This holds true for certain verbs in a pretty idiomatic kind of way. For other verbs it is rather unusual. If the word has developed into an adjective, it often also develops comparatives and superlatives: vervelender, vervelendst etc. Some adjectives -particularly compound ones- do not occur as verbs at all like hartverscheurend, bloedstollend.
Notice though that the sentence "dat is bepalend voor .." does not have the meaning of a continuous tense as it would have in English. It means something like "this is decisive for .."
Continuous aspect -if it is at all rendered in Dutch- usually takes verbs like zitten, staan, lopen, liggen + te + infinitive: "ik zit de volgorde te bepalen". Alternatively you can use a aan+het+infinitive construction: "wij zijn aan het bepalen wie dat gaat doen".
Present participles are quite common as adverbs though: hij ging fluitend naar zijn werk. Luid zingend liepen zij de straat door.