Lets have a closer look at the features of the three cars:
Elantra GL: 1600cc, 126hp (civic X 2017-2021 Oriel=140hp), manual one zone ac, sun roof, fabric seats, auto dimming head lights, key start
Elantra GLS: 2000cc, 154hp, 2 zone auto ac, auto dimming mirror, power seats with lumbar, sun roof, fabric seats, cruise control, rain sensing wipers, auto dimming head lights, 6 speaker entertainment with apple car play and android auto, eco/norm/sport/smart modes, (not sure if it has e-brake or not)
Civic Turbo RS 2021: 1500cc, 174hp, single zone auto ac, sun roof, leatherette seats, remote start, paddle shifters, cruise control, rear entertainment screen, norm/eco modes, e-brake. Hope I haven't missed out anything important.
If the civic turbo RS didn't have a 1-100 acceleration of just over 7 seconds, there really isn't much going for it compared to the Elantra GLS. IMO the Elantra GL is way too basic.
With regards to the drive and feel of the Elantra, ask the showroom for a test drive.