Goal contributions across all club competitions for the three players in question, covering the season they joined us and the 3 seasons prior, making no comment on and no allowance for the quality of the competition, time spent injured, or freak events like Grealish getting 2G 3A in one match against Liverpool last year. With their age at the start of the season in brackets after the season, for a little context.
Mahrez:
15/16 (24) - 18G 10A = 28
16/17 (25) - 10G 7A = 17
17/18 (26) - 13G 13A = 26
18/19 (27) - 12G 12A = 24
The year he joined us his goal contributions equalled 92% of what he achieved the previous year and 101% his average of the previous 3 years.
Bernardo:
14/15 (20) - 10G 4A = 14
15/16 (21) - 7G 3A = 10
16/17 (22) - 11G 12A = 23
17/18 (23) - 9G 11A = 20
The year he joined us his goal contributions equalled 87% of what he achieved the previous year and and 128% his average of the previous 3 years.
Grealish:
18/19 (22) - 6G 8A = 14
19/20 (23) - 10G 8A = 18
20/21 (24) - 7G 12A = 19
21/22 (25) - 5G 3A = 8
The year he joined us his goal contributions (so far!) equal 42% of what he achieved the previous year and 47% his average of the previous 3 years.
This tells us 3 things:
1) Judge his numbers against his record, not the others'. I'm working on the assumption here that we bought him knowing and liking his skillset, not expecting him to be something he's not. So yeah, his first season he's got a third as many GAs as Mahrez got the year he joined. But Grealish's annual average return before he joined us was 17, where Mahrez's was nearly 24. So we surely haven't bought him expecting him to return Mahrez numbers (although we should be looking to push him to around 2 thirds).
2) That said, he has struggled to deliver the numbers this year. I don't necessarily think it's the big crisis some make out. Goals and assists are the bread and butter of football, he wants them and we want them for him, but nonetheless it is possible to contribute in other ways and (although he's often been frustrating to watch this year) I get the impression - from what he and Pep have said, from the game time he's been getting which is broadly on par with Mahrez and Bernardo's first seasons, from Pep's general attitude towards him - that he is grasping what's been asked of him and contributing in other ways (as the link
@plebhead8 shared demonstrates)
3) Mahrez and Bernardo both saw a slight dip across both goals and assists the year they joined us compared to the previous year. Jack's seen a similar dip in his goals stats, but what's really hit him is his assist numbers have collapsed.
I think the absence of a real striker has hurt, because he's got no previous experience of providing for a false 9 or any system where there's no up-front focal point. Where Mahrez, Bernardo and the rest at have learnt that system alongside the rest of the team and had years to acclimatise to it gradually alongside players they know well, working out how best to play in the system, Jack's been thrown into an established system and has found it hard to work out how to maximise his talents.
Jack got 12 assists last year, comparable to both Mahrez and Bernardo the respective years they joined us. Both those years, we had Aguero scoring 30+ goals, not to mention our other players chipping in for fun. Villa's top goalscorer last season was 16-goal Ollie Watkins.
I don't think he's ever going to score a shit load of goals for us. But give him even a half-decent striker and he'll smash the assists.