The decks described in the OP do cover a lot of strategy advice for newer players. It is an important thing to learn that once your turn 9 engine is doing something to figure out where to go. First there is the reliability/payload balance and keeping control. And you also need to know if you are going for 2 province per turn buys which need overdraw or that you can save up more payload for a megaturn.
In the case where the turn 9 deck starts adding more draw for green space or starts adding more bridges or HoPs for a megaturn, I don't see why these aren't different types of decks. And I can imagine there are kingdoms where it is unclear what route will lead to the win, thus making the pursuit of either deck a distinct strategy. (and not 'just things people play that are wrong' like you mentioned before, though that was about 'hybrids').
The thing is, this applies universally to all engines:
1. Trash as much as you can. Add in the absolute minimum economy that you need for the purposes of step 2.
2. Add more draw until you can draw your entire deck reliably or you can't add any more draw.
3. Add payload while accommodating for it by adding more draw until you reach the point where continuing any further doesn't really improve your deck anymore or you're forced to green due to tempo concerns.
4. Try to end the game in a win (well, you should do this as soon as you can even if you're not done with the previous points, but that is not how you're initially planning to have it work out).
The case in which the turn 9 engine can start adding more draw to prepare for greening or adding Bridges to prepare for a megaturn is no different — if you have enough time that you aren't forced to green immediately, you add the Bridges every time, and if you don't, you don't have time to make your deck more reliable either so you just green immediately in that case and hope to get good enough draws. After that point, you repeat this exact same consideration every turn (sometimes, this might even manifest in the form of having to grab one Province to prevent your opponent from ending the game, then continuing to build as usual).
If Bridge or other way to improve your payload beyond 1 Province/turn isn't available, you can spend some time in step 3 for just adding reliability to your deck if you have the time, and green when the returns get too diminishing, or just green as soon as you have to.
I really can't imagine a kingdom in which you would ignore adding more payload for any reason other than the tempo concerns. The payload helps you add more components to your deck faster, so you should end up with a deck that's not only able to buy more things per turn, but is also more reliable than you would if you just added a couple of extra components in order to have room for green cards.
As a crude example, let's say your deck is: 1x Lab, 2x Gold, 1x Silver, 1x Chapel. You have to start getting a Province every turn after two turns. You are essentially getting a 6-card hand every turn, except you only have 4 stop cards in your deck right now, so you have room for 2 more stop cards, which is not enough for all the Provinces you want to gain. You could buy a Lab this turn, another Lab next turn and then start to green — that would give you enough room for 4 Provinces (plus a 5th one that you don't need room for because you'll never draw it), but during the last shuffle, you could get screwed by having a Lab at the bottom of your shuffle. Alternatively, you could buy a Bridge this turn, a Gold and a Lab next turn and then start to buy Province+Lab turns, giving you enough room for all the green cards you ever want to buy and you will always have 1 extra room for a stop card (you could still get screwed, but it's much less likely), and on your last turn, you can buy Province+Duchy instead of Province+Lab and this takes exactly as much time as the former alternative.
