Well I'll assume you're just shooting from the hip with your subjective opinion here and haven't actually bothered to check the numbers, because they paint a very different story to the 'unreliable, terrible and rarely hard working' 2020 you've described:
Aiden Tolman in 2020:
Games: 17
Average Minutes: 61 per game
Tackles: 685 @ 93.8% efficiency, which incidentally, is a comparable efficiency to the likes of noted gun defenders McCinnes, Twal, & Jake Trbojevic
Average Tackles: 40.8 per game with an average of just over ONE missed tackle per game in the second worse team in the comp.
Average Run Metres: 18 runs @ 141 metres per game
Discipline: 3 penalties conceded and 5 errors in total in 2020, which places him amongst the lowest for these numbers for any middle defender in the competition.
Put simply, if you were to compare Tolman to the Broncos in 2020, no Bronco has averaged as many tackles as Tolman, no Bronco has as high a tackle efficiency as Tolman and only Payne Haas has averaged more metres gained. I'm sure I also don't need to point out that our only even close to comparable players in Haas and Carrigan also have more errors and penalties conceded too.
Sorry to break it to you, but whilst he is perhaps not a gun player or likely to get much better either, the idea that Tolman is declining or just isn't good anymore is frankly not even remotely supported by the numbers.