Very few 4Xs get combat right anyway. Tactical combat is cool but if it's poorly done, it just gets repetitive and annoying. Good example: the remastered Master of Orion, in which the tactical battles are a disgrace. Not that MoO1 and MoO2 had spectacular combat either. It's probably best to avoid tactical combat altogether and instead focus on the strategic.
The important thing is that ships and fleets have distinct roles, and you aren't just throwing like against like. GalCiv 1/2/3 and Endless Space both shied away from tactical combat, and both suffered immensely because the bare bones combat mechanics that remained were shallow, anti-fun, and anti-depth. Terrestrial 4X titles without tactical combat don't seem to have this problem very often (and also tend impart more importance on terrain and positioning), while space based ones usually do.
That said, I feel that there's something to be said for complexity when it comes to combat mechanics. When you have a complex enough rule-set, such as, say, BattleTech, you can derive depth organically through the novel interaction of the myriad variables that can come into play over the course of a game. And then when you enter the competitive sphere you then also have the benefit of a fluid and compelling metagame. This is ideal.
Of course complexity in itself is not a good thing, and should typically be minimised when possible. So when I make the case for complex combat mechanics, it's not with the view of making things as complex as possible, but with the resignation that a certain amount of evil is necessary and it is difficult to create deep systems without a good amount of underlying complexity (at least, unless you get
very abstract).
In terms of design:
Fluid, organic, novel variable interactions > pre-defined roles > simple value check > mechanics that actually hurt depth
(In the real world this is actually more of a gradient than it is distinct classes)
My argument in favour of tactical combat is that if you were to try to create a deep rule-set where the background simulation would take place, without the ability to go in and tangibly interact with it, you're basically doomed to failure. So you probably either need a previously established rule-set that is already battle tested, or you need somewhere to hone and refine your rule-set. In Dominuns Galaxia, we have working tactical combat but it isn't all that good yet since the rules and mechanics are still being fleshed out, but we also have the ability to auto-resolve any encounter, and you can auto resolve at any point during the event. I feel that is the way to go since those that love tactical combat get it, and those who hate it don't but are left with a deeper strategic game all the same.
But I dunno, the archetypical 4X has basically three different stages that should all be interesting and exciting and hardly any game has even gotten close. You need to have lot of micro things to do at the start and it's cool to get nitty gritty with the details. Then you get to the middle portion where you don't really want to fiddle with asteroid mines because you have bigger fish to fry. Finally you reach the late game portion where your stellar empire is big enough that you only need to focus on the macro level. I think the best 4X games have gotten two of those right but nothing has gotten all three.
You don't need a lot of micro at the start. If you want a bunch of stuff to fiddle with and touch, there are plenty of mobile "games" that fill that void. If you want to solve math puzzles, there's Sudoku. 4X design is about two things: maximising depth and feeling like a bad ass emperor. Busywork accomplishes neither.
Game can simply limit the number of actions/orders player can do/issue per turn. So, he can command small kingdom/army by himself, but has to resort to AI governors/barons/generals later.
To me this seems arbitrary, but also feels like a band aid. You aren't really increasing depth, you're lowering frustration, weakening immersion (because of the arbitrary, abstract, and altogether game-y nature of the mechanic), and probably hiding real issues (eg. unnecessary busywork, inefficient UI, etc.)
A tweak that makes the idea far more compelling is to handle "action limits" organically instead of arbitrarily. So, for example in a real time setting you might introduce a communications delay based on the distance between any location and the position of your avatar. This means that there is no restriction on player actions, but that commands work better the closer you are to an asset. After a certain point, the delay in receiving information combined with the delay for that asset to receive an order makes direct micromanagement impracticable to the point of lowering performance instead of augmenting it.
The bigger problem with 4X games is design. When eXploration is finished, there's little left for you to find out. Then you start optimization of your empire. And why do you optimize? So that you could conquer more land. Then you optmize new land so that you could conquer more. You're basically stuck in an endless loop until the game ends.
There needs to be different stuff to do in game, and different ways to win, if applicable. I'm not talking about Civ style victories, which are mostly a red herring, but different playstyles. Not all parts of the map should be equally interesting to everyone. If you're building a trading empire, a single island/planet might be extremely important trade route for you, but just a useless piece of rock to someone else. Your government type or policies or culture or religion might make some area manageable for you but a nightmare for someone else.
When it turns to just whoever controls more map has most money and best tech and largest army, it becomes boring as soon as you acqure critical mass.
I agree with your initial assertion, but I'm not sure if I agree with the rest (simply because it's too easy to interpret what you wrote in a few different ways). In general, I'm not a fan of multiple victory conditions. Part of it is that multiple victory conditions have a tendency to be band-aids for bad design: Either the conflict driven core of the game is fundamentally lacking, so give the players something to distract from that, or at a certain point the game simply collapses under its own weight, becomes drastically unfun, and giving players the ability to "opt-out" early makes it more difficult to reach that point.
I also think that there's a ton more elegance in "one goal, many paths to get to it" than there is in "a handful of paths that are largely divorced from one another." So, for instance, I would find a technology victory more appealing if instead of immediately "ascending" and cutting the game short, you were to gain some form of massive military advantage that let you quickly mop up the remainder of the map that still left some room for counter-play after acquiring it (maybe another empire is frantically working on their own super weapon, maybe someone steals the deathstar plans, or maybe the rest of the galaxy unites against you and wins via sheer brute strength, etc.)