For a novice player that is grinding trough the low and medium tiers to go to GLOPS or the other PvP mode brings some problems.
He has to fight against humans and not stupid AI driven bots, some of those players are more experienced then him, most of them already have high level commanders and possibly some very good premium one, like Cortez for maxed damage, O Connell for superior camo or Ophelia that allows suicide tactics that seems that the present GLOPS meta rewards, as i see them so often. They also can have full grind tanks with lev 4 or 5 crew and possibly high level retrofits.
Our hypothetical grinding noob friend will have many disadvantages to deal with, further on if in PvE the team will win probably 90% of the missions if not more in PvP, no matter how you are good, you will sit on something like a 50% win rate, if you are good a little more, if you are not a little less, but the time of the skirmish mode, that gave to 3 people in platoon the chance to farm easily wins is long time ended (and I am very happy of that).
It is true that in GLOPS to win and do well is very rewarding, but you win less and not all the players are over the average, so I am not so convinced that the suggestion is useful for everybody, it greatly depends on how a particular player is really willing to learn how to play and gifted at it, then he can probably overcame the other disadvantages with a good playing and be well rewarded the 50% of the matches he wins.
But your suggestion IMO is very good for an other reason, playing PvP you will suffer more, a lot more at the beginning when you are still learning, but you learn much faster and much more. I would say that the better mode to play to really improve is Random Battle, and if you have the luck to play against strong players and are smart enough to play near the good players of your party you learn a lot, GLOPS is a lot more forgiving as you can respawn, but you learn less, still learn how to fight, both tactically, reading the minimap and reacting to how the battle is going and how to act in close combat, when you face an other MBT, when you are flanked and circled by a very mobile enemy or when you have the mobile tank and do the trick yourself. In PvE the point is to understand how a program works, what the bots are scripted to do and when and where they will spawn, then, once you have learned how to play a particular mission you are almost set up to go, and you will improve much slower then in the PvP modes.
So I think that the suggestion to play GLOPS as soon as possible, if you are lucky to live in a place that make possible (time zones and ping problems), to do it you will certainly become a better player doing it and eventually you will also be rewarded if you manage to become an over the average player, one that when the party wins sits on the high side of the ranking in spite that he is probably playing a tank without retros, with a low level commander and a tank that you are still grinding, so not full upgrade and with a low level crew. Even if you don't manage to become so good your PvE playing will anyway get much better, as you had been forced to actually use your brain and polish your skills, so you will any way be more rewarded in it.
EDIT: if the new player has a good, GLOPS wise, T8 premium tank it is surely very good to play GLOPS as soon as possible, even using it to play only PvE speeds so much the grind of the commanders and makes getting credits not an issue for all the low part of the grind, but the money, commander XP and reputation he can get in GLOPS are much superior, as well as the rewards for the Special Operations. Having a T9 or 10 tank that can play Heroic and being in a battalion as there the rewards are massive and every Heroic run is a big improvement in the commander xp and in your credits income, and you can do it every 3 days, even if it counts for the battalion contract only once a week, but to get a T9-10 tank means to participate to the box lottery or to buy the gold to get the T40, in both the cases we are beyond the scope of this whole thread, while a good T8 costs a lot less and potentially can be the only real money a player has to invest in the game, while still making the first part of the grind a lot faster and less painful, with enough credits to buy the progression tanks, to equip them with some retros and some reputation to spend at the beginning of the grind of each tank, ie to unlock fast HEAT and so boost the damage that tank can do.