Well nothing is ideal for everybody. And you certainly shouldn't train all the rep zones and types in every workout. But you also need to understand that some type of contractions can potentiate other.
For example... doing heavy work (1-3RM) will potentiate work performed in the 3-6 zone. So by combining both you actually get more out of the 3-6 zone.
I find that doing work in the 3-6 rep range with enough volume improves the quality of speed work done AFTER. This is especially true of people who are decently explosive to start with. If you are explosive, you can actually create too much acceleration from the start of the concentric action. This forces you to start decelerating sooner. The result is less top speed and spending more time decelerating than accelerating. If you are fatigued from heavy work (but not pumped like crazy from high rep work) you can't create as much acceleration from the start and you will actually be able to accelerate for a longer part of the ROM. Making speed work more effective.
Explosive work (jumps, throws, Olympic lift variations, jump squats, med ball throws) can potentiate heavy work (1-3 reps).
So the proper combination of various contraction types CAN make the training more effective. But one thing I noticed is that the more different types of contractions you have, the harder it is on the CNS.
For example this morning I did a pressing session:
A. Military press with cambered bar 15 x 1 @ 85% with 30 sec of rest
B. Close-grip bench press with cambered bar and 75lbs of chains per side ramp to 3RM
C. Eccentric overload close grip bench. 70% on the bar but an additional 20-25% of my max on weight releasers, lowering the bar in 5-6 seconds. 15 sets of 1 with 30 sec of rest
D. Close-grip triceps death set: around 60%.. max reps, then without rest max reps off of 2 boards... 3 sets
And then 2 triceps isolation exercises for sets of 12-15
Felt great, good performance all around, but I did have a mini CNS "down period". And it wasn't the volume (15 sets sounds like a lot, but they are submax singles) since I've done more volume with less CNS impact.
So one has the weight the pros and the cons