a. Block size - This was increased in bitcoin cash. What many people are not aware of is the paper 'Information propagation in the bitcoin network' by Decker and Wattenhofer in 2013. The average time for a block to be seen by a node is ~13 secs. As per the paper:
"For blocks, whose size is larger than 20kB, each kilobyte costs an additional 80ms delay until a majority knows about the block." -'Information propagation in the bitcoin network.
So, increasing the block without increasing the block time actually increases chances of double spending. But, increasing block time is well simply delaying the payments.
b. Lightning network - Off-chain transactions. Fascinating idea. The problem is it goes to a form of centralization. And if things hold the companies running these channels will invariably meddle in some transactions. But the stated goal of bitcoin was -
Commerce on the Internet has come to rely almost exclusively on financial institutions serving as trusted third parties to process electronic payments. While the system works well enough for most transactions, it still suffers from the inherent weaknesses of the trust based model. Completely non-reversible transactions are not really possible, since financial institutions cannot avoid mediating disputes. The cost of mediation increases transaction costs, limiting the minimum practical transaction size and cutting off the possibility for small casual transactions, and there is a broader cost in the loss of ability to make non-reversible payments for nonreversible services. With the possibility of reversal, the need for trust spreads. Merchants must be wary of their customers, hassling them for more information than they would otherwise need. A certain percentage of fraud is accepted as unavoidable. These costs and payment uncertainties can be avoided in person by using physical currency, but no mechanism exists to make payments over a communications channel without a trusted party