Look at the label on the 'power supply' which came with each of those LEDs.
There's a reason its's called an "LED Driver" and not a "Power Supply".
That box supplies a constant Current to the LED, not a constant Voltage because LED brightness depends on Current, not Voltage.
LEDs are 'non-ohmic' devices which means they don't follow a linear voltage/current relationship like an old incandescent light bulb.
Measuring the output voltage of one of these drivers with no LED connected will only tell you what the maximum voltage is that it can provide with no load - not what it will provide when it's actually driving an LED at its rated current.
Measuring the voltage with an LED connected will tell you what the characteristics of that one particular LED are and should not be extrapolated to other LEDs.
By applying a constant voltage to your LEDs and not controlling or limiting the current (other than the 6A overall limit of your new power supply), it's entirely possible that you've already damaged some or all of them.
Remove your 24V 6A power supply, put the original LED Drivers back on, and hope the LEDs still work ...
The only reliable way to run these LEDs off a single LED Driver is to connect them all in series (not parallel) so that they all have the same current flowing through them (and therefore the same brightness).
The single LED Driver will need to be able to supply a voltage of at least 7 x each LED's nominal voltage (because the voltages add up when they're in series).