Yup. As long as you don’t need them logged in at the same time then training alts on the same account is very useful. PI, research, hauling, market, etc. And then as you said you don’t need to pay to maintain an extra account.
Also if you use Plex you will notice the multiple training certificate on the new Eden store is cheaper than a month of game time. So it can be cost effective to train other characters on the same account at the same time then stop training them once they are at whatever skills they need. Then they still can use them as Omega as long as you maintain Omega on the “main” of the account.
Even if you use +5 implants and a remap to train, the cost per sp using the MTC for the alt is way less than injectors especially as the alts get to higher sp levels. Of course you can also pause your main to train the alts as well if you don’t care about simultaneous training.