Based on the provided financial facts and the S&P methodology for Regulated Utilities, TenneT Holding B.V. is a transmission system operator owned by the Dutch State, operating under a regulated framework. This provides it with highly visible and predictable cash flows, characteristic of a "Strongly Suitable" hybrid issuer.

Analyzing the financial metrics for the fiscal year ended December 31, 2022:
1. **FFO to Debt**: The company reported a Profit Loss From Operating Activities of -976 million EUR and Finance Costs of 300 million EUR, totaling an operating loss for the period. While EBITDA is not explicitly given, the negative operating profit implies severely depressed or negative FFO. With Total Debt (Long-term + Short-term Borrowings) of 19,715 million EUR, the unadjusted FFO/Debt ratio is negative, falling significantly below the S&P 'BBB' threshold range (typically 12%-15% or higher for regulated utilities).
2. **Adjusted Leverage**: TenneT already has 2,125 million EUR in Hybrid Capital recognized in equity, demonstrating both a historical precedent for hybrid issuance and the market's acceptance of treating these instruments as equity-like capital. Issuing additional hybrid bonds would directly and materially improve the adjusted leverage (Debt to Capital) and FFO/Debt ratios, providing crucial rating headroom.
3. **Funding Rationale**: The company is undergoing a massive capital expenditure program, with 4,424 million EUR spent on PPE in 2022, leading to a significant FCF deficit of roughly -4.1 billion EUR. The funding need for capex is strong and clear. Furthermore, the existing hybrid capital of 2.125 billion EUR will eventually approach its call dates, creating a refinancing rationale.
4. **Financial Policy & Market Access**: As a state-owned essential infrastructure provider, TenneT possesses high credibility in financial policy and reliable access to institutional capital markets.

While TenneT's fundamental business profile (regulated utility, state-owned) is extremely strong, its current financial metrics are deteriorating due to heavy investment and negative operating profit in the reporting year. This aligns perfectly with the criteria: "Deteriorating financial metrics per S&P and hybrid needed to preserve current rating" and "Hybrid issuance could materially improve adjusted leverage, FFO/debt, or rating headroom." 

Thus, a hybrid bond issuance is highly suitable and strategically necessary to maintain its Investment Grade profile amidst heavy capex growth.

<answer>Strongly Suitable</answer>