Its with the realms of possibility.
the easiest way to do it, is to not log in or play much, so your stamina use is way down, that means you collect more stamina each day and it will stack. I have had over 900 stamina on one account and there is also the stamina rebuy, the recent stamina item compensation the more you save, the more you can use at once....
Spend during the events. that will give you the eidolan glass needed for the 2x 5 stars that they have
Level up the home, and the hot springs for increased stamina regen.... you do not have to be online all the time to level up the housestead
Using the daily quests, stadium etc for exp from level 45 to 51, is not that hard.... its actually only 4 levels if you look at it .. you can be almost level 46, and just get level 51, so you only actually need to get 46 to 50 in exp which is not as much as 6 full levels.
The eidolans they have, would give them a big boost in gauntlet so running that with the eidolans would give them a higher level and more rewards, also in stadium which also means more rewards and also in campaign and skrimish
and you can get a lot of exp from stadium
now by checking the rankings, they are not listed for purple items on their eidolans... so its logical that a lot of their BR is actually in mounts..... so if I check the BR which is just over 500k BR and their exp level which is just over level 51
They are up to tier 10 woodland sprite which is possible using the eidolans they have.