I occasionally find MP regen rate a problem, but in 100% of those times it's due to my own mistake in not potting early enough. Focus more and pot earlier and you'll be fine.
For example say you're about to use 6000 MP worth of spells in a short period of time, you'll be wanting to use a 6000 MP worth of pots to finish on the same MP you started.
Let's say you start at 3000/4000. Don't start wait until your MP is 1000/4000 before using your first 3000 MP pot. If you know the spells will use MP faster than the pots work anyway, just hit 6000 MP worth of pots straight away at the same time as you start casting and your MP won't hit max until you've finished casting and cleared the area you were working on.
A real life example. I know that to clear a bile/totem room takes me approx 8000 MP, now my max is about 4100 but that doesn't even matter. As soon as I start hitting I know I'm not stopping until the room is clear, so as soon as I've cast my first spell I'll hit 8000 MP worth of pots then I can relax and know that I won't be running out and can safely continue to focus on my attacks. It's good to have one less thing to worry about
Obviously I understand in more open situations your mp usage can't be calculated or predicted quite as accurately as that, but the same theory applies. You see a lot of mobs, you can estimate how many pots worth of MP they will take to clear, drink all the pots you think you're going to need (overestimate! No reason to guess low, plenty pots to go around) as soon as you've engaged with your collection of enemies. Then you'll be fine!