Achieving 2mio XP per day is not unrealistic if you are prepared to grind high XP advs that can be completed fairly quickly, over and again.
To give an insight, I like to churn 1T, 3T, SLT, and ofc, Tikkis.
I can easily grind:
3T, tikki - approx 1.5 - 2hours for both.
SLT, tikki - approx 2hours for both.
Given that 3T+Pandas is worth ~420k xp, SLT+weddings is worth ~205k xp (I know you can't guarantee follow ups with SLT), and tikkis are ~120k xp, in a day of gameplay you can easily be approaching 2mio. Now add on all the LS pandas, and weddings, and 2mio is easily achievable.
Of course - keep L6 Barracks AND Elite Barracks skunk'ed 24/7, and recruit guides come in handy from time to time
Whilst doing this I buy every SLT or BLT LS I can get at normal price.
The faster you can grind an adv, the faster you can gain the xp and loot and start another - time is my most crucial resource.
With Tikkis - I ONLY do them them between advs, whilst waiting for TVGs to arrive home from the last adv. This means having 6 fast gens at home specifically for Tikkis.
I use 3 MoDs, 2 BHGs and a LD, but if you have only 2 MoDs, you can use a BHG for the penultimate attack.
Tikki settings I use:
Of course - being able to grind something like a 3T is crucial to fast XP, so I have set out below how I do it. This is NOT intended as a guide to blindly follow, but more an idea of how using every gen you have, sometimes at the cost of slightly higher losses, with the minimum amount of wasted time on movement, you can complete advs in record times. You can adapt this methodology to other advs, like WoodCutter, and to an extent SLT, with minimal movement (this is a 1h15m adv, LSers dependant).
* 1R Block is sent to L8 for interception by C24.
There is also the option to use more gens to complete all attacks without buffs, but of course, we need more gens - it can be done, but I prefer the easy option of buff killing L9.
Hopefully you will have an insight of how 14mio a week is not unrealistic, IF you have (most importantly) the time, the resources, the gens, and the pop required to keep high numbers of troops available. This method is not for everyone, and grinding the same adv over and again CAN get dull, but I do other advs too ;o)
Oh, and don't forget your crystals for long-letter quests! And also at L70 you get to make approx 120k - 150k xp a week on Pathfinder and also get 5k Starcoins - perfect for all those buffs you need to buy from merchant.
... and before anyone points out you can't buy more than 1 ROA a day and only 1 Assassin every 2 days - they are 'giftable' if you are wiling to pay for them with gc
Happy XP hunting... and please don't berate me for any mistakes in the above guide. I haven't had it proofed and you use at your own risk hehe