Disc brakes for daily use: recommendations

Hello there!
I got a Diverge E5 Sport for my daily commute and found it awesome! My problem started when I require my brakes to work. It's a (mechanical) Tektro Mira disc-brake, which I've found hard to pull-in (I need to use 2 or 3 fingers on STI) and still they aren't very responsive.
I did some "warm-up" pushing in-and-out STI levers in order to brakepad get used on the new disc. It's a little better now, but its still noisy, unresponsive and tough to activate.
I also have a road bike with Ultegra (groupset) with rim brakes and wow - so smooth, nice and effective.
Is there something I can do to improve my disc brakes to make them more "ultegra-like"? The bicycle is partially-equipped with Sora R3000 groupset 2x9 (STIs and derailleurs). I'm searching options in order to keep this change cheap as possible - a.k.a: to not change STI to 105/Ultegra to support a hydraulic disc brake, for example.
Thanks in advance!
I got a Diverge E5 Sport for my daily commute and found it awesome! My problem started when I require my brakes to work. It's a (mechanical) Tektro Mira disc-brake, which I've found hard to pull-in (I need to use 2 or 3 fingers on STI) and still they aren't very responsive.
I did some "warm-up" pushing in-and-out STI levers in order to brakepad get used on the new disc. It's a little better now, but its still noisy, unresponsive and tough to activate.
I also have a road bike with Ultegra (groupset) with rim brakes and wow - so smooth, nice and effective.
Is there something I can do to improve my disc brakes to make them more "ultegra-like"? The bicycle is partially-equipped with Sora R3000 groupset 2x9 (STIs and derailleurs). I'm searching options in order to keep this change cheap as possible - a.k.a: to not change STI to 105/Ultegra to support a hydraulic disc brake, for example.
Thanks in advance!

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It’s new. I bought a week ago and rode 50miles with it.
I have 2 week or so new bike myself with cable disks, the brakes did feel stiff for the first few miles, it’s a CX/adventure/gravel bike and been wet, so I’ve assumed that the gritty first ride nicely bed the pads in. Either way the disks shouldn’t feel stiff, possibly be worth checking with who you bought from?
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