It’s well known that most manufacturer claims about mass produced antenna products are somewhere between BS half truths and total ■■■■■■ sci-fi ludicrous.
The only ‘gain‘ figures worth a light, assuming they ain’t fiction, are gain relative to a half-wave dipole, since isotropic radiator relative gain figures (usually quoted as they look better) commonly used with vertical omnidirectional antennas are relative to a hypothetical radiator which would be dubious if it actual was built and laboratory tested.
So, a colinear’s gain relative to a vertically polarised half wave dipole antenna has some sound grounds to be credible. Likewise a corner reflector (as used as a compact high gain antenna on wifi or she usage) was genuine gain vs the dipole as do multi-element beams and co-phased or composite arrays of colinears vs a vertical dipole.
So working upwards, a 1/4 straight vertical is worse (even when optimally mounted) because it’s dB lossy vs a vertical dipole and more so as it’s emitted EM lobes spread the energy in many directions emanating from the driven element.
Optimally mounted, a half-wave dipole is unity gain (0 dB), so you ain’t going to see true passive gain until you move towards a colinear and then (optimally installed) you are into gain that’ll count for something. Similarly, focused directional antennas (parabolic, corner reflector and yagi beams) have gain advantage over a dipole in degrees of focused nodes that focus the EM nodes towards a narrower aperture of emissions.
How much difference a gain change, and bigger received signal makes or worsens very much depends on mode of transmission, especially on digital to critical degrees where SQ matters not absolute received Sig strength.