” and could not find anywhere in halacha where it says that there is a distinction to be made between the three weeks/sefirah”
I think I answered you on that and showed you a few mareh mekomos in halacha. Now I have a question for you, I can not find anywhere in halacha that is mattir. Who is this respectable rav? And how come every time someone has a psak from a daas yochid against rov haposkim come from an anonymous name? And how come an anonymous name is enough to make as if there is no inyan at all?
also i think I left out a few mareh mekomos. The Magen avraham 558:1 , and the mishna berura 558:2 also mentions kli shir. Also the pri megadim (aishel avraham) 558:10 talks about the issur of a kli negina ( not in a case of rikud) and so does the Derech hachaim in hilchos bein hamtzarim sif 1 , The biur halacha 551:2 dh ummatim, shu”t chaim sheal siman 21, maharam shik yd 268 butchachersof siman 552 and the shevet halevi 2:57 8:127. and in haaros from rav elyashiv on gittin daf 7. kovetz halachos bein hamtzarim perek 4 etc. so i think it is a generally accepted halacha.