I think I'm just playing on a standard difficulty. The combat plus map exploration and unit growth just takes so long.
If you don't enjoy the combat you could try auto-resolving your way through less important battles (it's also calculated differently so it can sometimes be used to get better results than you would in a tactical battle). You don't have to focus on upgrading units (more on just keeping medalled ones alive), it will happen naturally or you'll find an arena.
AoW2/SM:
~ worse music (you can add AoW1 music to it though), worse campaign, worse screen resolution and UI,
~ map scripting (more plot-heavy maps) and more background map objects, IMHO uglier units,
~ random map generator,
~ more granular city upgrading/growth limits per city but in practice it's heavily underused so instead of cities having different and fixed sizes on maps like in AoW1, they will all look the same eventually,
~ shadow realm with permanent haste and debuffs for most units instead of deep caves,
~ worse city/tower battles (especially that you can just punch the gates a few times to bring them down without any wall crushing ability) and dungeons with a few props in the open in the middle of the battle map instead of underground fog-of-war corridors) - makes visiting these faster though,
~ AI worse at casting enchantments,
~ has dragons and catfolk instead of lizards and azracs (+ a few other races like wtf syrons and shadow demons), less uniform looks of armies of different races,
~ shipyards moved into cities (but AI cannot into naval warfare so it doesn't matter), there's building new cities instead of new watchtowers, cities also have buildings letting you teleport between them and craft custom artifacts,
~ leaders don't level up and have to stay in wizard towers (also respawn on death if you have at least one such tower in one of your cities),
~ more RPG elements (e.g. random fetch/kill/raze/conquer sidequests from city shrines) and city upgrading (AoW1 is almost solely focused on army movement and combat), doubled stat limits,
~ most ranged attacks let you move at the same turn at the cost of less attacks being made (e.g. archer shooting one arrow instead of three after moving to the side because of the enemy unit hiding behind a rock) so that may make the combat a bit faster for you (no need to optimize your positioning to not waste archer turns),
~ up to 8 players vs 12 in AoW1.
~ from cheesing, instead of making uber immortal leaders (bonus points for siding with lizardmen in the campaign and crippling the AI by casting flood), flying ships or carrying a doom priest with you between missions, you can take your sweet time at the beginning to craft all the artifacts you may need (boring).
Both are worth playing, though (and you may find the combat different enough to like it more in the sequel), and AoW2 has better mod/total conversion options (especially that Age of Glorantha mod).