Lest say if I was in charge of re-doing the simply-jetpacks mod, and I'm still using tiers.
There would be 4 tiers:
1) A bootstrap/intro tier (jet-packs don't need to be bootstrapped like vanilla pick-axes, so "intro" would be more descriptive in this case)
2) A workhorse tier
3) An advanced tier
4) An OP tier
The bootstrap/intro tier would be really cheap to craft, like; wood logs, a potato with a redstone dust.
It would have a reasonable speed, no armor, and about 20 seconds of flight in total. It would use durability instead of charge, and break when used up. This tier could be disabled in the configs.
Someone could craft a couple of these early game and use it to explore, just by being really careful in its use.
The workhorse tier would require you to tech up, just like the existing version of the mod. It would function like the IC2 jetpack, have an option to add armor plating, and can be used with a glider/elytra for fast horizontal travel at low energy cost. It would be rechargeable, and have a large enough internal battery to use it comfortably.
The advanced tier would have hover mode, allowing it to be used for building more easily.
It would not have armor options and can't be combined with a glider/elytra.
This means the advanced tier is not very good for exploring.
The OP tier would combine the good of both the workhorse and advanced tire and none of the bad. This tier could be disabled in the configs.
Its purpose would be to provide something for players that like OP tiers, or for progression based modpacks such as AgeOfEngineering, that need something for their End-game.
The mod would function just fine with this tier disabled, since the two main tiers are designed to be good enough.
See... Tiers, even progression, but each tier is unique. Not just more of the same, but with higher stat value.
Alternatively, I could replace the advanced tier with a helmet, and have the helmet provide the hover mode to the jetpack, but enabling hover mode interferes with the glider/elytra. You'd still have armor plating, but the helmet has a low armor value. That would get rid of one more tier.