For several year i've played classical guitar in the traditional way...but some year ago i've fallen in love with the sonority of nylon guitar played with only the fingertips.

So, i've cut my fingernails and started to rebuild my right-hand technique from the ground up.

From the beginning I realized that when I play without fingernails, my left hand work harder.

My hypothesis are focused on the greater force that the right hand imprints on the strings.

Hypothesis confirmed by reading the writings of Emilio Pujol.

In his "Escuela Razonada de la guitarra", Pujol says (screenshots taken from an italian edition):

The string respond immediately to the action of the nail and the fingers of the right hand get the desired effect with minimal effort.

It follows that the resistance of the fingers of the left hand is significantly lower, because not necessary.

...and about the "no-nails" approach:

The fingertip is a soft body, wider than the nail and therefore, by pinching the string, it must make a greater effort.
This effort necessarily requires a greater pressure and resistance of the left hand to overcome the pressure of the strings.
It follows that the barrè, the scales, the slurs, the extended positions and certain virtuosic passages are more difficult with this procedure.

And finally a sentence that sums up my choice to play without fingernails:

Considering that the sound must be a means rather than an end, the guitarist will have to choose one and the other of the two procedures according to the style and character of the performed music.

My suggestions

Train the left hand with slur exercises, but also Giuliani's "120 arpeggio" could be a training tool: the chords kept during the execution of all 120 exercises is a very good muscular training!