I was looking at the dimensions of the Fuji Altamira (Fuji Bikes | ROAD | COMPETITON SERIES | ALTAMIRA SL). You mentioned a fuji altimax, but I know of no such creature. The L has an effective top tube of 57.5cm, while the L/XL is 59cm. So, there is 1.5 cm difference in effective top tube.

If one looks at the Frame Stack and Reach dimensions (which I tend to find more useful than effective top tube) on the same webpage for the same sizes, the frame of the L/XL will, all other things being equal, place the headset 20mm higher but 8mm farther forward.

I would expect the reach to be about 8mm more on the L/XL with the 59cm top tube. If that is too long, the other model might work better. The only way to know is to ride the bike. If you like the front end of the bike higher, the L/XL may be better, and you could downsize to a 110 mm stem.

Was the salesperson wrong? I can't really say. His insistence on the L/XL seems a bit misplaced without having you on a bike. How tall are you? What is your cycling inseam? Maybe the salesperson saw someone well past the threshold for a L/XL size but maybe you are less flexible and prefer less reach.

As to the other bikes you mention, you can find the same dimensional information on their manufacturer's websites.