I think the theory is that if you're gonna completely remove holds from stuns, then you also need to have SIGNIFICANTLY fewer attacks cause critical stun, with the bulk of attacks simply leading to various amounts of hit-stun granting the attacker various amounts of frame advantage for following attacks. And the stuns left in should grant some window for landing a guaranteed launcher or knockdown or something. Critical burst would then need to be taken out as well, since it would be pointless and overkill in such a system. Sidesteps would also need some buffs ... and the game ends up becoming something closer to a VF clone.
If what you want is not a VF clone, then you leave holds from stuns in. Now, personally, to improve the system here, I think it would be nice to see extended stuns have some unholdable properties, and attacks landed during the frames of a whiffed hold putting the opponent in an extended stun state (up to max threshold). For example ... opponent gets stunned, immediately low-holds, gets hit by a mid to extend the stun, is now unable to hold for ~15 frames, and the attacker can either go for a critical burst (if fast enough), a fast launcher or knockdown, or jab to extend to max stun threshold and finish however they like. This kind of setup provides a "penalty" for whiffing holds, granting certain guarantees to the attacker. Also, I think the deeper a stun goes, the longer the opponent should be prevented from holding (~15 frames on 1st extend, ~20 frames on 2nd extend, ~XX frames on critical burst).