I do not know if it's available on iOS (I suspect no) but on Android I am a really happy user of Osmand. It uses Openstreetmap as maps provider and I always use it when hiking. It gives you the altitude profile of your route which is very useful.
I also use Osmand, though when I compared it to Maps.me, loading a map was significantly slower in Osmand
2. Disable map features like areas, buildings and such
3. If still unhappy, delete the full blown map data and download the road only map data (about ⅓ size of full blown map)
4. eMMC/microSD speed matters a lot, if you put it on an external SD card, make sure to get a high speed IOPS card labeled "A1" (1500) or better "A2" (4000 guaranteed read IOPs).
Reason: The map is rendered locally on demand from the map data(base), there's no tiles in the default map view. You basically get almost all of Openstreetmap's data (POIs, buildings, areas, ways and relations), not every poi type is indexed and searchable though. It even have has a working public transport map with routing based on timetables (if present) and ferry ways, etc. If you put the data on a slow external sd card, you'll notice.