150w OMtech, output power varies, lower than usual mA reading after 500hrs

I have no idea.

My opinion: a laser tube can be “good” in only one way and “bad” in many different ways.

Perhaps using a target more durable than tape will allow slightly higher power with shorter pulse times. The controller should allow setting the single-pulse duration, as described in the early part of this discussion:

Setting it for few tens of milliseconds should produce a distinct char, rather than a hole: tune for best picture.