If Towers are nerfed they are also nerfed defensively. If there is no difference between building a tower infront of the enemy base or in your base than it will either be OP in offence or useless in defence.
AoE4 has a lot of mechanics that would make Tower Rushes much stronger than in AoE2. If there were no limitations the Meta would be all Tower Rushes at last in the Mid range skill level.
Yes a pro can defend against a Tower Rush but it would ruin the game for a lot of people that never have the chance to become a Pro because they are stuck getting Tower Rushed every game.
As I sad, hard limitations are not fun.
It would be better to add positive mechanics that improve the defensive usage of towers instead of limiting or removing the offensive potential.
They could give the Town Centre (or later Castle) a buff for near towers, make them cheaper, build faster, more HP, more attack or more range.
Not removing the option for offensive Towers but making them weaker than defensive ones.
Delhi Infantry can build Tower, that clearly shows the Developers want Towers to be used offensively to some extend.
I think the was Strarcraft did it was smart but can’t be applied to AoE4 directly.
Having to build a Pylon first delays your Cannon rush, giving the enemy more time to react, it makes it more expensive and it makes the Cannons more vulnerable. Cannon rush is still (at last back when I played) a viable strategy but not overpowered. If Cannons could just be build everywhere they would be OP.