Maybe I should have rephrased that to "Solidly" justify it. 20-30 ish extra mana early levels is not a strong tangible advantage, even after splurging flat mana runes trying to shore up his mana pool, to consider going that route over the EXP buff. Not gold efficiency wise, not in game impact wise. The EXP buff isn't something immediately tangible like damage health mana etc, but it's universally better than an extremely small boost to your mana pool, EVEN for characters that scale better than everyone else with mana. In stats gained from mana or how many more spells they will be able to use because of it.
If you want to state an opinion or offer something, go ahead. If you want to convince someone that Yorick is good, that he was better than previously thought, then offer up something that strongly supports that. Gameplay matches, strong player opinions and discussion, something other than "Well this is what I do personally and I think it's a good idea." I don't just say Yorick is bad "Cause I said so", there's been a plethora of widespread community talks about Yorick being quite weak and having issues compared to anyone in his class. With comparisons of his base stats and spells to other champs, strong players using him and trying all sorts of different builds, theorycraft over damage (realized and potential), etc. All of it leaned towards the character being fairly bad.
As for the max mana part: I used the max mana pool part as an example, not as something you specifically said. You went on about how the boost was nice, and I said "Well even if it went off Max mana, using a mana pool he will never reliably reach 95% of the time, that the number he would get from that falls short of a 400g Sapp Crystal. So, getting an even smaller boost than THAT high "inflated" number doesn't seem worth it".