When you see all the ball strike marks dead center of the sweet spot. If you can't do that yet, stick with more forgiving sets.
At the end of a round do you talk about your score or what clubs you played?

There are players of all handicaps playing the T300/350. Blades don’t necessarily improve your play.

Replacement is primarily a distinction between need and want. $1500 for a new set can be the deciding factor. I might think I want Miura irons, but that never gets past a want. I can think of a couple of thousand reasons.

Assuming scoring 95 included some miss hits/off center strikes, you may be getting the sweet spot more often. Upgrading your irons to get a different feel and easier to shape shots gets you closer to a need. The trade off is forgiveness. If you went to a Titleist sponsored fitting, they will work with you to see which T-series iron works best for you. Not every pro even with a negative handicap uses 620 MB. So look into an upgrade but get professional recommendations, not a bunch of guys that could hurt your game.

There are PGA tour pros that play blades and others that play T100’s and even T-series combo sets. If the best play whatever works for them, so should you. Maybe experiment with different T-series options with a good fitter but nothing wrong with sticking to your T300’s if you continue to be happy with the results.