Quote from Chihaya;1288173:
Except that Synthesis DOES have the easier equivalent called a "Synthesis Training Potion" when the RNG gets on your nerves that you can purchase for 2-3m on Tarlach. For MC/Engineering, you need 450 Seals for ONE RANK which is worth roughly 8-10m (again on Tarlach) considering 350 nets you an RK armor that sells for that much.
Or 210~280 seals per rank (Roughly anywhere from 3.6m(RKs go for 6~7m here, taking the lower amounts) to ~4.4m(selling enchant de-expires for 250k/ea)). Add 25% to get to the 280, resulting in 4.5m to 5.5m approx. Mari server.
Then you can use a few hours instead of a few days to get crystals from the heart(via glitching there or using aggro lock), gather several bags of shyllien, and make bullets>processing and finish off 45/60 points of the rank and save yourself half the nightmare of sealing it all.
Sealing via adventure seals is also horrendously wasteful if you do it entirely or at all in some cases. Engineering less so, because you HAVE to farm around 2000 total cores to rank it iirc. There's no french hell sick enough to justify doing that. 10m in seals is nearly a fourth of either of the two skills' mastery on 4x. Including the shyllien crystals/Hillwen fragments. I ranked on 2x the entirety of magic craft without once thinking about seals, and engineering I used them because they were event, I had nothing else, and because I wasn't resilient or strong enough to farm a couple thousand cores or buy them.
Mastering Synthesis, not to mention, while small in counts seems no less horrendous than mastering engy/MC