For consideration, the rules I have my players use includes 300xp for apprenticeship (150 + 150, just like the old days). Strong Parens/Weak Parens is an option on top of that. Post gauntlet development (I allow elder magi) equals on average 10xp per season, and a season in the lab grants 2xp Exposure.
As a comparison: I have a character that started out using core RAW, was retconned using JL's house rules, and was retconned again latter using mine. Three different sagas over the course of six years or so. In all cases, advancement opportunity is much better in a live saga compared to even my generous HR's. In Novus Mane, the original version using Core RAW, I was able to hit 10xp or more a season on average. In Bibracte (Mon Electi), I was able to hit those averages and higher and had a much more powerful Aura for lab work. In Andorra, using the rules there, I struggled to hit my marks and keep even with where he was and would have been at various stages. These are the stats for Roerto in 1235, in the Light of Andorra saga. If he would have stayed at Mons Electi and played through tp 1235, he would have been a bit more advanced. The plan I had laid out for him there would have taken him to a minimum score of 5 in every Art and equipped him with another half dozen spells.
Which is just to say that I think upping XP slightly for newly gauntleted magi and for advancement beyond is perfectly reasonable and does not unbalance anything.