My last GM considered my sorc casting firebolt an abuse... cuz he did not like cantrips being used to attack folks every round...If players can abuse the initiative system the issue isn’t with the initiative system it’s with the game one is running. Player abuse isn’t a system issue. It’s a DM issue.
I use a similar system with roll over monsters. 6 PC 5th level 1 vs. Orc with Pie. Maybe the orc gets lucky and the rest of the table laughs at Satyrn Sorcerer as he wipes Split Pea Pie off his face. Maybe not.The system as written.
For a while we were doing a group initiative, where the Players got their turn and then the DM took his. On the Players turn, each character acted in whatever order the players wanted, switching it up each round however they pleased. Obviously, it optimised their actions (so the guy with Shield Master would go before anybody else attacking the same foe) and that was the draw that made the system fun. Plus, it meant I never had to track initiative order as DM.