i think there are some diffrent consideration how to build your roster and or how you wanna play the game .
first things first
a roster of 6 chars which you basically equilly push up to 1430 is the best and most cost effective way atm
and then after you did that then you push your main
so if you spent all your gold and mats for your main before you pushed alts to 1430 , you lost alot of potential , but also sure its not done from now to then . its a time investment.
pushing from 1430 to 1460 with event books and that stuff is then the way how you cost effective push your alts.
if you know the content you dont need 5x3 and lvl 7 gems for a 1460 char and doing all the content . 4x3 and lvl 5 gems ist more than enough ( sure gatekeeping could be a problem , but thats not the theme here right ?
if you spent your mats and gold for 4-6 weeks into your 5 alts which are 1415 you reach easy the goal to get them to 1460 , but not all at the same time, push one at the time
every alt take atm 12 weeks to make profit from that investment , means after 3 month an alt your pushed from 0-1460 give your extra gold/mats for your main
from 0-1490 ist 5 month that your have that back
so there are 3 ways in my opinion , dont play alts above 1430 to make your main stronger , which is timewise more effektive
or if you like playing your account as a whole push that characters you like and play them
or invest time money gold what so every make yourself a strong roster as fast as possible and a few month later it snowballs that hard , that you dont need to spend alot of time and money/gold whatsoever
thats what i did in summer , i pushed 8 characters as fast as possible to 1460 , and now i dont have to consider how i get stuff for my main , and only play what i like… im not even doing every raid with my alt
( also the guys you see which packed roster mostly dont invest time in their alts they invest time into the market place to increase their gold and with that time they spend , i personally doing that 30 minutes daily , you can make so much more gold than doing raids with alts you dont like)