It is a very old and solid idea. I've always been in favor of just this solution.

I'm also very fond of the changed summoning skill system where you get bonus based on level you gained the ability.

I.e. You get Thunder Spark at 19. So at 19 you have 0 skill over cap natively. At 29 you have 30 skill over gained ability level cap. At 39 you got 60 skill over cap.

This would allow old pacts to "grow" with power along with your levels. We are of course not talking massive damage boosts to Thunder Spark here, since after all we just said it would be on a 20 sec recast. But we are talking things like 5 min duration crimson howl (if anyone cares about that) or 5 min ice spikes etc.

Also another change that is needed is to scale some potencies. Like Nocturnal Shield should be -15 when gained, but then increase with like -1 per 10 skill (or roughly 3 levels) past the level we got it. I've forgotten when we get it, but assume 45, and it would mean we get roughly -30 on it at 90. A nice boost to make it useful at high levels.