Yes, XP gain is a grindfest and I completely agree that the 'learning limit' where your multiplier can hit x0.00 at some point needs to go. I'd go even further and suggest that the whole levelling system needs a complete overhaul.
There are too many skills that are completely irrelevant to your combat oriented companions and things like scouting only affects the guy you gave the role of party scout to. Eventually the XP gain for lots of skills will grind to a complete halt for your companions. Both the player and their companions are forced to fill up their XP bar by doing all kinds of stuff. It's impossible to excel in a set of 2-3 skills by doing only the relevant activities because it would take forever to get the necessary focus and attribute points this way. Also, getting attribute points only once every four levels is a travesty.
In Warband we had skill stacking within a party to a degree, e.g. your party had a trading, scouting and engineering skill that was affected by your top guy in a discipline but also got a bonus from the 2nd best guy.