That's not true at all. Adding a single tool can change the durability or threatening ability of a character in a way that forces the other character to interact with the differently.
Meta is not a single-character concept. Metagame is totally dependent on matchups. There are tons of new matchups that Melee top characters have to deal with in PM. Each one of those is new meta. And even among Melee:Melee matchups, all characters ahve changed subtly, including all of them gaining RARs, b-reversals, actionable ledge jumps, special+airdodge interruptible IASA frames, and sometimes slightly changed normals/throws. Any time one of those things is different for one character, it's different for both characters in the matchup. Marth's dair has less landing lag, now he can tech chase spacies with it. He has RAR, now he can turn around more quickly before jumping offstage for edgeguards. He has b-reverse, and can interrupt fair endlag with with specials, meaning SH fair side-b fair, and SH fair b-reverse/wavebounce side-b fair work. None of that's possible in Melee, and it's all unexplored in PM. That's just for one character, who was barely changed at all outside of the port to the new engine, and it affects all the matchups he's involved in.