But the utility of 071s is to project amphibious force at much longer ranges than Taiwan, whenever China needs to seize territory anywhere else in the western Pacific, SCS, etc.... many of the "alternatives" people listed aren't able to substitute for that.
If it's true 071s cost only in the $2-300M range I think it's a no brainer to double the fleet & provide much more options in those regards.
Just because they (071/075/076) are capable of conducting Amphib Ops at far longer range doesn't mean they are restricted to that.
Any Amphib Ops, even an uncontested landing, requires specialised units trained to operate in rather exceptional circumstances to establish and expand a beachhead that is capable of receiving subsequent waves from less specialised units. Yes, it doesn't take much to train a grunt to climb in and out of a AAV/ LCU/LCAC but the command and logistics capability required to move, form up and amphib assault is quite specific. Hence you need these amphib assets and units to be the first couple waves and once successful, the requirements are a lot lower for subsequent waves (who basically then take a "taxi" to the beachhead).
Even if the range is short, even if it is just a coastal hook, civilian watercraft do not quite suit the load plan of a military unit nor allow them to deploy coherently offshore to conduct a landing in a coherent fighting order. They (civ assets) are more suitable for what they are designed for - cargo, which means taxi service for subsequent waves on an already established bridgehead.
Even if the cost of each additional Type 071 is low, resources are not infinite - both in terms of what can be afforded and what can be deployed.
Consider the current fleet of 4 Type 075s and 8 Type 075s, Grouped into 4x Amphib Grps of 1x075 and 2x071s each, you have the capability to (rough math) lift 3 Bdes (assuming 3 Grps up and 1 down)
Consider also the opportunities for a Div sized landing and if there is none then multiple Bde landings at different AoO, which will then necessitate even more surface combatants to escort the multiple Amphib Grps (on top of other requirements to man CSGs and SAGs)
Can the PLAN afford extra hulls? Outright, money won't be the problem. Crewing? Don't know if PLA will run into staffing problems that other militaries have. Requirement? This is where maybe there really isn't one ... What is the likelihood that the PLA and PLAN, in current stance, has the need for multiple Bde or even Div sized landings anywhere? What is the likelihood that the PLAN has the force structure to prosecute this and support this expand Amphib fleet (don't forget you need to maintain supply lines to those beaches/islands/continents you just landed on).
Requirements will always dictate the design and quantity of platforms ... something we always seem to forget when we do wish list of what PLA should be or should have.