also, the best resource I know of for interactive help is the forum at pd patch repo... https://forum.pdpatchrepo.info/ the community is the largest I have found and the help is probably more helpful and less snarky than other routes.
I think it is entirely possible with FOSS. this kinda reminds me of the situation 10-15 years ago when people were trying to make their windows laptop look like a mac... because mac was more "respected" in audio circles... FOSS will work for professional audio... how many sneers and eyerolls it solicits from others who paid $$$$, who knows.. prob a good bit depending on the circles you roll through.
for reference, here is a video regarding getting VST plugins inside of Pd.
https://youtu.be/Cs0NPime0kU
this guy has some excellent videos regarding Pd in general...
although he hypes-up "dangers" of Pd regarding feedback, the clip~ object will nullify that
your title asked "can you only use Pd" and the answer is yes, but not many people do.
the thing is it is capable, it can just be alot of work... and so much effort and attention have been given to VSTs that alot of people just cannot give them up to learn how to build a from-scratch reverb.
the Erbe-Verb , named after another UCSD professor, Tom Erbe, is a digital reverb unit for eurorack but before he coded the algorithm in C, he designed and built it for testing and fine-tuning in Pd. Pd, much like any synthesis programming language is plenty capable... its just that it requires alot of work which, for some, is very irritating office-feeling-kinda-work and not making music.... Pd is like that for some people... and so Pd is really not worth getting into if it does not provide you with some option or ability that you could get more easily with a plugin... especially if plugins are your jam to begin with!
i hope that babbling helps!
hello from the bottom! lol a rabbithole indeed!
there is another channel, "cheeto moskeeto" , that has been helpful and is often recommended, but the tutorials are 12 years old and i believe he uses Pd-extended so alot has changed, but still worth a look... https://www.youtube.com/playlist?list=PL12DC9A161D8DC5DC
thanks for your time! all the best!