5W-30 is really a good thing and highly recommended - to support your oil dealer's or garage owner's income...
All these old Mazda engines from the 80s and early 90s were built for that older days standard oil types, 10W-40. That's really enough. With "better" (or let's say more expensive for truth) you will never feel any difference. In fact, there will be no benefit for your engine. It's better to have regular oil changes instead of using an expensive oil.
IMHO: when so many people are using 5W-30, the marketing and the oil lobby have done their jobs excellently
And yes, of course, Mazda-dealers have to recommend 5W-30: they have the nice, amazing, powerful Mazda Dexelia oil. Only the best oil for customers cars... and for profit maximisation on the side of the Mazda dealer, Mazda itself and Mazdas oil producer, TOTAL...
Simply use a good 10W-40, not the cheapest, and anything's fine.