When you say last set, do you mean the top heavy set, or the final drop sets?
Yes.
If using DropSet the lead-off set should be a 3-4 rep max taken to a rep shy of failure, then dropped to a maybe an 6-8 rep max taken to a rep shy, finished with an 8-10 rep max. Using a high rep load for the kick off completely defeats the purpose of Drop-setting and by your last "set" puts you in a rep range where contractile force is limited by buildup of inorgnaic phosphate. This is going to have negative downstream implications for tendon remodeling, firing rate, unit recruitment - everything. If you have joint issues or equipment limitations this is still a valid way to train, it just leaves low-hanging fruit unpicked.
You'll get hypertrophy from a lower starting weight but it is all metabolic stress, and your training time more than offsets any longer or additional rest periods used with heavier loads. There may be some benefit for localized endurance as you'll be depleting muscle glucose to a greater extent although using LESS of it! (IIRC Upregulation of the Cori Cycle triggers anabolism) This almost certainly increases uptake/storage capacity over time, but not independent of glucose to contractile protein %. IDK - this gets into "sarcoplasmic hypertrophy" which isn't really supported by much of the research at the muscle fiber level but might be explained by other larger factors - like tendon remodeling.
Rest/Pause taken to a less than failure per, and Clusters are almost identical in application with the only difference being the number of repeats, how you determine the starting number of reps per, and how you do decide when to terminate the Cluster. For notable Hypertrophy there almost certainly has to be some form of fatigue degrade happening - ie "I didn't hit my target reps this repeat", or just drop load and do an immediate run-out set, assuming your initial sets are at a fairly high % of your rep max - per DropSet recommendations.
Rest/Pause and Clusters have a massive advantage in practical terms as they don't require micro-loading. Sets of 5-6 rep repeats seem to work just as well as sets of 2 rep repeats, and allow for a lot more volume than one could otherwise get at those load ranges. Big shout out of thanks to
@kennycro@@aol.com for advocating Clusters - I'm sure they can be used with anything but they work brilliantly with my sandbags. If I were eating more I'd probably be pushing my heaviest lean mass ever and at a higher load to bodyweight than even a low rep DeLorme strategy.
Either approach, using the fastest possible concentric rep speed seems to be an additional multiplier for strength with no downside for hypertrophy. Important -
this is not the same as intent to move rapidly. The rep speed needs to actually be quick at least for the initial sets. This also means you need to be using a fairly heavy load, frenetic jerking of light weight is NOT the same thing at all.
What would be the minimal number of exercises you think would still be effective for hypertrophy?
I'm honestly not sure, if talking about balanced physique and musculature you need minimum horizontal push, horizontal pull, hinge, squat. Trying to build a lot of mass using only four exercises is probably suboptimal but I'm positive it could be made to work.
Coming back to the same movements over and over is going to accelerate the "repeated bouts effect" and probably overload the body's ability to make the best use of post exercise muscle protein synthesis - you NEED downtime just as much as you need a credible stimulation. If you're limiting the number of exercises, then by definition you are not doing anything else on your downtime even though there is capacity to do so - just not another helping of the same.
Extending the horizon for results is a possible way to mitigate this, but is just managing higher density blocks or jumps spread out over more time.
Another factor to consider when going minimalist - the exercises you DO chose need to be high systemic demand compound lifts. These tend to give a big knock-on effect hormonally which is great, but they also tend to need more recovery mentally and physically if used for hypertrophy. You can easily feel this when doing a workout - something like a double front squat will require far more rest than one arm press for similar TUL.
Having 4 primary lifts and another 4 auxiliary lifts is about as minimal as it gets if hypertrophy is a prime or 1:1 objective. This allows for increased frequency, hitting the same muscles but not in the same movement patterns and with other muscles picking up the lion's share of the tension. Alternating use of big compound lifts and secondary (also compound lifts) that are not as demanding is a good way to go. Added advantage of being able to alternate focus, deloading one to increase load or volume on the other.