lets handle black hatters cons
more time required for verification... LIE
nodes verify 99% of blocks as they are relayed pre confirm.. nodes can handle hundreds of megabytes (as proven by bitcoins node mempools of each node.. and funnily enough devs own admissions that nodes on mainnet and subnetworks can sign and pass millions of transactions a second)

mining becomes less competitive... LIE
there is more to the reward vs fee vs market price economics than just "tx pay more"
16000 X $1 (using unified 4mb instead of segregated 4mb) = $16000
4000 X $2 (usual segregated 4mb when not spammed) = $8000

as you can see mining can get a bigger fee bonus by letting in more transactions without having to cost users more

and by the way.. every time there is a halving idiots think this is the time to 2x+ the fee's to offset the reward halving.. another lie..
its actually where the MARKET increases to compensate the reward halving. but that makes fee's $ more so fee's need to decrease to prolong bitcoin utility and desire of people to want to use bitcoin..

if you want to keep the bitcoin market alive you need to keep BITCOIN usable. otherwise people move over to altcoins that have the same crappy subnetworks. but have cheaper fees

trying to suggest halt bitcoin growth and promote subnetworks solves nothing. because people will just use the same subnetwork. but with an altcoin as a the settlement..