Can the shown figure actually be compared to a TVS diode?
A TVS has a similar function as two regular diodes, but the ESD current can be shunted to ground instead of one of the rails. The diagram above is mainly for overcurrent\overvoltage protection. A TVS has a higher breakdown voltage which is mainly useful for very high voltages such as those from ESD. You probably wouldn't want the ESD spike ending up on your power rails, even with a limiting resistor, so a port to the outside world should have TVS diodes close to the entrance of the input to the board to shunt the currents directly to ground.
If so, can the functionality of TVS diodes be improved by adding the current limiting series resistance and a bulk capacitance?
See this answer TVS diode before or behind resistor :
You have three components there that are all there for protecting the
AVR, but all are doing a different job.
The resistor is there to stop steady state high voltages.
The capacitor is to remove ripple/RF/slow transients.
The TVS is to suppress fast transients.
In order to get the best out of your protection, you need to have the
shortest (lowest inductance) path back for the fast transient impulses
(such as ESD). To do this, you fit the TVS (the fastest responding
device) as close to the input to the board as possible. The capacitor
would then be a bit further in (depending on the layout and design)
and the resistor (which only deals with very slow, or steady state
situations) can pretty much be on the pin of the AVR
Why aren't any of these improvements suggested in the datasheet just like decoupling or bypass capacitors are recommended in every IC
Because the IC datasheets don't know what the designer is going to connect the ports to. Most IC pins are connected internally on the board, and don't require extra protection. They do specify what not to do to the IC in the absolute maximum ratings section and in the ratings section for different pins. To provide this information on every datasheet would provide too much information. This information is provided in the form of app notes as it applies to many different IC's
Analog: Solving IEC System Protection for Analog Inputs
and Using ESD Diodes as Voltage Clamps
ST micro: https://www.st.com/content/st_com/en/support/resources/resource-selector.html?querycriteria=productId=CL1137$resourceCategory=technical_literature$resourceType=application_note