BUG: PerformanceWarning when agg with pd.NamedAgg and as_index=False

[xma08]

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• I have confirmed this bug exists on the latest version of pandas.

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Reproducible Example

import numpy as np
import pandas as pd

n_rows = 1_000
group_size = 10
n_random_cols = 200
data = {"id": np.repeat(np.arange(n_rows // group_size), group_size)}
for i in range(n_random_cols):
    data[f"col_{i}"] = np.random.randn(n_rows)
df = pd.DataFrame(data)


# PerformanceWarning when as_index is False
named_agg_without_index_warning_df = (
    df
    .groupby('id', as_index=False)
    .agg(**{
        column: pd.NamedAgg(column=column, aggfunc="mean")
        for column in df.columns if column != "id"
    })
)

# no warnings when as_index is True
named_agg_with_index_ok_df = (
    df
    .groupby('id', as_index=True)
    .agg(**{
        column: pd.NamedAgg(column=column, aggfunc="mean")
        for column in df.columns if column != "id"
    })
)

# no warnings when using dict agg no matter what as_index is
dict_agg_ok_df = (
    df
    .groupby('id', as_index=False)
    .agg({
        column: "mean"
        for column in df.columns if column != "id"
    })
)

Issue Description

there is an inconsistent behavior (PerformanceWarning) of agg when as_index is True/False. Please refer to the example above.

Expected Behavior

No PerformanceWarning is raised when as_index=False

Installed Versions

v2.3.0

[arthurlw]

I did a little bit of testing (using time) and found that using dict agg with as_index=false is actually faster than named agg, so I am not sure if a Performance Warning is necessary for this case.