Would not a circular saw on one arm and a trowel on another on the Mars 2020 rover add scientific value?
Every different type of thing you can do has "scientific value", even if it proves that it's not a good idea something is learned; it just that it's less expensive to learn that on Earth.
A circular saw on a telescopic arm with the ability to cut into hard soil at different angles and a trowel to remove the loose soil on another arm, with both arms on the front of the rover could meet this demand.
Size weight and power (SWaP) is considered for things aboard a spacecraft that are smaller than an image sensor. A circular saw is by definition 60% useless, you can't use half of it yet it weighs twice it's usable cutting edge. The telescoping attachment adds more weight as does the telescoping shovel to chase after it; also there's the scooping and packaging mechanism that is not needed for a core drill.
This is what a saw on a telescoping attachment capable of cutting rock looks like:
A smaller one could be devised but you can still only cut ~40% of the saw's diameter.
Of course the rover has already a core drill, but that's designed to take samples with very advanced techniques and needs very careful working.
The pdf you linked to: "ROPEC – ROtary PErcussive Coring Drill for Mars Sample Return" explains:
"The ROPEC Drill design builds on previous drilling systems such as the Mini Corer, Corer Abrader Tool, and SASSI Drill; improving upon them to achieve a light weight, compact, and highly capable mechanism.
The ROPEC drill is designed to support a “One Bit-One Core” approach to delivering rock samples to a sample return canister. This method dedicates a single drill bit to the acquisition of each returned rock core, as shown in Figure 1. After the core has been separated from the base rock and captured within the drill bit, the entire bit is delivered to and stored within the sample cache in an enclosed casing, to ultimately be returned to Earth. This method simplifies the process of caching rock cores by eliminating additional mechanisms required to extract rock cores from drill bits and place them within sealed canisters.".
It cuts out core samples almost the full depth of the drill and stores "grade A" cores intact. No transferring or contamination. It's also easy to change bits for different hardness and density, avoiding fracturing as best as possible.
Linked article's conclusion: "The ROtary Percussive Coring Drill is a light weight, flight-like, five actuator drilling system prototype
designed to acquire core material from rock targets for the purposes of Mars Sample Return. The ROPEC Drill is designed to integrate with a “One Bit-One Core” approach to returning samples from the Martian surface. The ROPEC Drill has a number of different attachments which expand its capability to include rock abrasion, brushing, powder and regolith acquisition, and viewing of rock cores for sample triage purposes.
The ROPEC Drill has recently been integrated with a five degree of freedom Robotic Arm and mobility system, and has demonstrated docking with a prototype Bit Station, obtaining a Coring Bit, drilling and acquiring a rock core sample, and delivering the bit to a prototype Sample Cache. All drill attachments have similarly been demonstrated from the same platform.".
While it might need improvement the decision of circular saw vs. core drill seems well founded.
Trying to saw out a pyramid of pyramids using a saw a bit bigger than 40 cm diameter is going to require 5 levels of 20 cm cuts, a total of 88 little pyramids of 4 cuts each - a total of 352 cuts, with allowances for the hub.
If you did that with 4 core drills with extensions, 6", 5 1/2", 4", and 3 1/2" diameter, your final drill on the fifth level could pull a 3" diameter core; a total of 5 cuts. Not only would you have to grab and throw each pyramid but there's a real danger of falling into the pit, something that wouldn't occur with a six inch diameter hole.
In addition not only is more than half the weight wasted on blade surface not involved in the cut but you are cutting three times as much rock just to cut the pyramidal section. Even with a single layer there's 20 cuts of more than 24 times the material. The wear of the equipment and energy to power such inefficient usage could pay for the core drill.
If you were cutting crescent moons you'd be better off than cutting wedges but it's not more efficient than a round hole. A straight line of stepped holes is going to get you deeper faster.