1) There is a 'buglet' in Bitcoin that means that you can construct a TXN that uses a lot of time to process / check. Let's not worry about what it is but agree that it exists. The larger the blocks the easier it is to construct this TXN, and IF we had 2MB blocks, right now, you could bring down the network. This issue is fixed with SeqWit. So Core thought, let's introduce SW first, THEN we can make the blocksize bigger. Safely.
Franky has a misleading understanding of Segwit, and jonald is a hired baboon. Franky1 will argue that this isn't fixed with SegWit, and he's partially right. The thing is (post Segwit):
1) You could use native transactions to abuse this quadratic validation time problem. However, you are not able to attack the network this way as using only native keys results in =< 1 MB block size.
2) This is fixed for Segwit keypairs and Segwit transactions as validation time is linear. Meaning, with Segwit transactions you can safely do >= 1 - 4 MB.
Pools can and will prioritize Segwit transactions over the native ones if an attacker tries to abuse this. It's a non issue.Eh!! If pool don't prioritise segwit then it is an issue. We have no idea how the pools may react in the future.