Drag n bite? Why use that when you already have lk bomber and cr.mp? I would suggest using center stage for fully screen j.hp/j.mp lockdown and pressure
I also believe like you that if you have "one type" of assist, that should be good enough...BUT... there is this thing called experimentation. And I was surprised to find that 3 lockdowns works pretty well and here's why:
You never know who will be alive on the team and who will be dead. Especially with this team since it has easy ways to safe dhc out from every character to every character. So say my double dies. Ok now it's squigly plus lockdown. Or what if my squigly dies? Ok now it's double with lockdown or painwheel with lockdown. This team no matter what composition always has lockdown. It doesn't lose that kind of resource. It also doesn't lose safe on block dhc and finally... I've simply never been great with gtfo assists and lockdown allows me to play heavy pressure and mass mixup rather than bait all day.
Also, this team does some really tricky and cool shit with these assists like:
Double:
Cr.lk,cr.hp,mp fireball plus dragon bite assist.
This is an UNPUSHBLOCKABLE string. And a hitconfirm. If its blocked double gets an easy attempt at a dash in low throw mixup for basically free. If it hits, drag and bite combos for so long that double can dash up chain into launcher xx hp shot, dash cr.mp,st.hk into full combo for seriously stupid damage.
...and that's from a non pushblockable string.
Then when squigly comes in, I've got divekick plus cr.mp assist confirm or simple sbo to install cheese. And when painwheel comes in if there are any characters left she has install plus sbo plus lockdown assist to help her out.
The team ain't perfect. But it's pretty good from where I'm sitting. Cause even with gtfo assists once I get hit I usually die... The gtfo means alot more in neutral than during resets. And these lockdowns are good for neutral as well.
I've also been doing double slide plus pw cr.mp assist. If it hits, pw wiffs and double gets full combo, if it gets blocked, pw locks down during double recovery and allows for further pressure.