That is how titles are won, a decent keeper and striker are a must in most title winning sides.
Most title winners have decent keepers/strikers but that's sort of implicit in the fact that if they win the league they clearly have a good team and hence probably good players in most positions, I don't think it's out of proportion with that. I can't articulate my point particularly well but what I'm driving at is that it's not like title winners are typically just OK teams with a great keeper and a great striker, they are just all round good teams with a high average standard of player meaning an average keeper/striker relative to their overall standard can be enough, they don't necessarily need a cherry on top of the cake if it's a solid cake to begin with.
I mean take Chelsea 2005, at the time they got the most points ever in the Premier League (way clear of what City will get this season even if they win every single match remaining) and their top scorer with 13 goals wasn't even a striker, second top scorer was Gudjohnsen who was OK but not what you would call top tier (probably not much better than Liverpool/Arsenal have today), and averaged less than 1 goal per 3 league appearances that season. Arguably the reason they dominated in the league (against an Invincible Arsenal team) was because they had a great squad depth, a great manager and were very well setup defensively including a holding midfielder.
I know you said most not all and as I said most winners naturally have good teams by definition, but that's just an example, MU won the league with a mediocre Barthez in goal, when Liverpool won the league the closest they had to a striker was Firmino (a #9 in the Jesus mould) who didn't even hit double figures etc.
I still think squad depth is important and that's one reason why City do so well, they have untold riches enabling them to accommodate missing players, rest players etc. I can't imagine Saka would get as many minutes at MC as he does at Arsenal for example.