Powering up Mewtwo

I recently completed my 7th ex raid and was blessed with a 93 IV Mewtwo, 12/15/15 While I was stoked to finally get a Mewtwo in the 90s, I was a little bummed he was a 12 attack. I'm wanting to power up a Mewtwo, but it's a huge investment. I've already got the rare candies put into him, and am sitting on about 350k dust. He'll max out at 3944. Should I power up this Mewtwo? I know it's only 3 attack points, 312 vs 315 for Mewtwo's base attack stat + my IV vs perfect attack IV.

I've also got a 15/13or12/11or10 84 IV Mewtwo. That's got the 15 attack I was hoping to get, but sub optimal stats otherwise. Maxes out at 3913/3914.

The only other solid Mewtwo is 13/13/14 89 IV, which maxes out at 3927.

The rest are 10 or 11 attack, 82 or sub 80 IV. So I'm not considering investing in them at all.

I'm not worried about movesets because I've got plenty of TMs to switch moves when needed or desired. I also realize this is first world pogo problems and wish the ex raid system was different for better inclusion. Thanks in advance, I really appreciate the input.