This boils down to how you see blockchain - do you see it more as a distributed system/infra or more as a one-of-a-kind global state machine. Of course, the real view is the hybrid of both.

Many ppl see blockchain more as the distributed system/infra and apply theories/technologies that are proved to be useful/valuable in the domain of distributed systems to blockchain. Sharding is a great example, which originated from database. Almost all popular databases (cassandra, gfs) that are currently in use are equipped with sharding as a feature which is great. It is a typical application of the idea of “divide and conquer” in CS. It would make a blockchain faster and has a higher throughput, perhaps a better user experience. The downside is complexity in terms of implementation. BTW, due to the decentralized nature of blockchain, FLP and CAP theories do apply, i.e., which is called impossible triangle by vitalk.

Some ppl see blockchain more as a one-of-a-kind global state machine that keeps perhaps most valuable information about this world about this generation of the human being. In that sense, tamper-proof (in general, security), anti-censorship (in generally, decentralization) demostratet the real value proposition of a public blockchain - something, such as database, distributed file systems, cannot provide tho they are fast, high performant and easy to use.

Since we are building a real public blockchain (i.e., IoTeX is not a pure distributed infra, at least the layer 1), we value security and decentralization much more than scalability, which can be addressed. Scalability would be useful only if the layer 1 is reliably and continuously providing security and decentralization, and scalability can be achieved in many ways IMO

on chain - basically hierarchical structure, to have multi-chains running on the side with the layer 1

off chain - ZKP with or without rollup, state channel, plasma (which only works for UTXO)

On the tech side, sharding itself is challenging:

Adds complexity in the system: properly implementing a sharded architecture is a complex task. If not done correctly, there is a significant risk that the sharding process can lead to corrupted global states.

Rebalancing data is non trivial: when a shard outgrows other shards and becomes unbalanced (a.k.a hotspot). In this case any benefits of sharding is canceled out. The ledger needs a re-sharding to allow for a more even data distribution. Moving data from one shard to another shard requires lot of complexity at protocol level (which hurts security potentially) and downtime (which hurts decentralization potentially).

State sharding is largely an unsolved problem even by Ethereum 2.0, it is at the research stage and not practical right now.

In general, my view is “sharding is not the proper tech for layer 1”.