Wolf: There are many Achronim (especially more Lomdish ones) who read the Rishonim like that. That the Ikkar of Tosefes Shabbos is just for Issur Melacha, not anything else.
mik5: It’s a Machlokes HaPoskim. There are Tzdadim both ways. And the Shmiras Shabbos does not always agree with R’ Shlomo Zalman, though the disagreements are very rare.