Very good record there! Lots of hard work has been put in for that (or else troll-lose results would not have been only 2 when there are usually a few trolls every season). To only concede 77 goals in 600+ matches require excellent team setup, and very well done! (Easy to score 10+ but a lot harder to set up a good team shape to get clean sheets at the same time)
In the long run, we probably still may be drawn up with equally talented managers who do the exact same manipulation trick, so by then we may need to be prepared to further strengthen in those seasons to keep the title-winning going. So short to medium term, it is way more feasible to build an ever-improving team with also draw manipulation in place to save packs up easier and quicker. (Or else money will run short too because of having to buy older players for squad).
Proper player training via draw manipulation would win against tanking teams in the long run as well. Tanked players would have greys improved (no reduction), while managers achieving successive promotions with all top scorer awards will gradually build a more specific-high-white teams with low greys as well. That is even before the manipulation team could widen the quality advantage by ‘filling in’ the supporting players (eg, say 9 key players of 140%% + 5x 1* vs 14x 90% - really no match when the former manager knows how to train players properly). For me, they can tank all they like because they would still lose very easily.