[2021] How is it possible that an AR with an SFOD Speedgrip allows for faster movement speed than an SMG with the same grip?

I’m a huge fan of the SFOD Speedgrip because I can run a bit faster than normal, something like Lightweight from older games.

But after the most recent weapon tuning update, SMGs with the final grip equipped somehow move slower than ARs with the same grip, and its noticeable to a point where I just don’t feel like running around with any of my SMGs because they just feel janky and clunky, compared to pre patch where they felt light and the best pick if mobility is a concern.

I don’t understand how this is now a thing. On top of being unrealistic from a realism standpoint, it’s dumb because SMGs are meant to be mobile unlike ARs and LMGs because they are lightweight weapons meant for rushing instead of picking people off from afar. When those weapons have slower movement speeds than SMGs, it makes sense because they’re not meant to be used with rushing playstyles, which SMGs are designed for.